Queryable.SelectMany 方法

定义

将序列的每个元素投影到一个 IEnumerable<T> 并将结果序列组合为一个 IQueryable<T> 类型的序列。Projects each element of a sequence to an IEnumerable<T> and combines the resulting sequences into one sequence of type IQueryable<T>.

重载

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>)

将序列中的每个元素投影到一个 IEnumerable<T>,它合并了生成它的源元素的索引。Projects each element of a sequence to an IEnumerable<T> that incorporates the index of the source element that produced it. 对每个中间序列的每个元素调用结果选择器函数,并且将结果值合并为一个一维序列,并将其返回。A result selector function is invoked on each element of each intermediate sequence, and the resulting values are combined into a single, one-dimensional sequence and returned.

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>)

将序列的每个元素投影到一个 IEnumerable<T>,并对其中的每个元素调用结果选择器函数。Projects each element of a sequence to an IEnumerable<T> and invokes a result selector function on each element therein. 每个中间序列的结果值都组合为一个一维序列,并将其返回。The resulting values from each intermediate sequence are combined into a single, one-dimensional sequence and returned.

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>)

将序列的每个元素投影到一个 IEnumerable<T>,并将结果序列组合为一个序列。Projects each element of a sequence to an IEnumerable<T> and combines the resulting sequences into one sequence. 每个源元素的索引用于该元素的投影表。The index of each source element is used in the projected form of that element.

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>)

将序列的每个元素投影到一个 IEnumerable<T>,并将结果序列组合为一个序列。Projects each element of a sequence to an IEnumerable<T> and combines the resulting sequences into one sequence.

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>)

将序列中的每个元素投影到一个 IEnumerable<T>,它合并了生成它的源元素的索引。Projects each element of a sequence to an IEnumerable<T> that incorporates the index of the source element that produced it. 对每个中间序列的每个元素调用结果选择器函数,并且将结果值合并为一个一维序列,并将其返回。A result selector function is invoked on each element of each intermediate sequence, and the resulting values are combined into a single, one-dimensional sequence and returned.

public:
generic <typename TSource, typename TCollection, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TResult> ^ SelectMany(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, int, System::Collections::Generic::IEnumerable<TCollection> ^> ^> ^ collectionSelector, System::Linq::Expressions::Expression<Func<TSource, TCollection, TResult> ^> ^ resultSelector);
public static System.Linq.IQueryable<TResult> SelectMany<TSource,TCollection,TResult> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,int,System.Collections.Generic.IEnumerable<TCollection>>> collectionSelector, System.Linq.Expressions.Expression<Func<TSource,TCollection,TResult>> resultSelector);
static member SelectMany : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, int, seq<'Collection>>> * System.Linq.Expressions.Expression<Func<'Source, 'Collection, 'Result>> -> System.Linq.IQueryable<'Result>
<Extension()>
Public Function SelectMany(Of TSource, TCollection, TResult) (source As IQueryable(Of TSource), collectionSelector As Expression(Of Func(Of TSource, Integer, IEnumerable(Of TCollection))), resultSelector As Expression(Of Func(Of TSource, TCollection, TResult))) As IQueryable(Of TResult)

类型参数

TSource

source 的元素类型。The type of the elements of source.

TCollection

collectionSelector 表示的函数收集的中间元素类型。The type of the intermediate elements collected by the function represented by collectionSelector.

TResult

结果序列的元素的类型。The type of the elements of the resulting sequence.

参数

source
IQueryable<TSource>

一个要投影的值序列。A sequence of values to project.

collectionSelector
Expression<Func<TSource,Int32,IEnumerable<TCollection>>>

要应用于输入序列的每个元素的投影函数;此函数的第二个参数表示源元素的索引。A projection function to apply to each element of the input sequence; the second parameter of this function represents the index of the source element.

resultSelector
Expression<Func<TSource,TCollection,TResult>>

一个应用于每个中间序列的每个元素的投影函数。A projection function to apply to each element of each intermediate sequence.

返回

IQueryable<TResult>

一个 IQueryable<T>,其元素是通过对 collectionSelector 的每个元素调用一对多投影函数 source,然后将这些序列元素的每一个及其对应的 source 元素映射到结果元素中的结果。An IQueryable<T> whose elements are the result of invoking the one-to-many projection function collectionSelector on each element of source and then mapping each of those sequence elements and their corresponding source element to a result element.

例外

sourcecollectionSelectorresultSelectornullsource or collectionSelector or resultSelector is null.

注解

此方法至少具有一个类型 Expression<TDelegate> 的参数,其类型参数为 Func<T,TResult> 类型之一。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 对于这些参数,可以传入 lambda 表达式,并将其编译为 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) 方法生成一个 MethodCallExpression,它表示作为构造的泛型方法调用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) 本身。The SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) method generates a MethodCallExpression that represents calling SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) itself as a constructed generic method. 然后,它将 MethodCallExpression 传递到 IQueryProviderCreateQuery(Expression) 方法(由 source 参数的 Provider 属性表示)。It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

因执行表示调用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) 的表达式树而发生的查询行为取决于 source 参数类型的实现。The query behavior that occurs as a result of executing an expression tree that represents calling SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) depends on the implementation of the type of the source parameter. 预期的行为是对 source 的每个元素调用 collectionSelector,以将其投影到可枚举的形式。The expected behavior is that it invokes collectionSelector on each element of source to project it into an enumerable form. 每个可枚举结果合并了源元素的索引。Each enumerable result incorporates the source element's index. 然后,对每个中间序列中的每个元素调用 resultSelector 所表示的函数。Then the function represented by resultSelector is invoked on each element in each intermediate sequence. 生成的值连接为一维序列。The resulting values are concatenated into a single, one-dimensional sequence.

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>)

将序列的每个元素投影到一个 IEnumerable<T>,并对其中的每个元素调用结果选择器函数。Projects each element of a sequence to an IEnumerable<T> and invokes a result selector function on each element therein. 每个中间序列的结果值都组合为一个一维序列,并将其返回。The resulting values from each intermediate sequence are combined into a single, one-dimensional sequence and returned.

public:
generic <typename TSource, typename TCollection, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TResult> ^ SelectMany(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, System::Collections::Generic::IEnumerable<TCollection> ^> ^> ^ collectionSelector, System::Linq::Expressions::Expression<Func<TSource, TCollection, TResult> ^> ^ resultSelector);
public static System.Linq.IQueryable<TResult> SelectMany<TSource,TCollection,TResult> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,System.Collections.Generic.IEnumerable<TCollection>>> collectionSelector, System.Linq.Expressions.Expression<Func<TSource,TCollection,TResult>> resultSelector);
static member SelectMany : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, seq<'Collection>>> * System.Linq.Expressions.Expression<Func<'Source, 'Collection, 'Result>> -> System.Linq.IQueryable<'Result>
<Extension()>
Public Function SelectMany(Of TSource, TCollection, TResult) (source As IQueryable(Of TSource), collectionSelector As Expression(Of Func(Of TSource, IEnumerable(Of TCollection))), resultSelector As Expression(Of Func(Of TSource, TCollection, TResult))) As IQueryable(Of TResult)

类型参数

TSource

source 的元素类型。The type of the elements of source.

TCollection

collectionSelector 表示的函数收集的中间元素类型。The type of the intermediate elements collected by the function represented by collectionSelector.

TResult

结果序列的元素的类型。The type of the elements of the resulting sequence.

参数

source
IQueryable<TSource>

一个要投影的值序列。A sequence of values to project.

collectionSelector
Expression<Func<TSource,IEnumerable<TCollection>>>

一个应用于输入序列的每个元素的投影函数。A projection function to apply to each element of the input sequence.

resultSelector
Expression<Func<TSource,TCollection,TResult>>

一个应用于每个中间序列的每个元素的投影函数。A projection function to apply to each element of each intermediate sequence.

返回

IQueryable<TResult>

一个 IQueryable<T>,其元素是通过对 collectionSelector 的每个元素调用一对多投影函数 source,然后将这些序列元素的每一个及其对应的 source 元素映射到结果元素中的结果。An IQueryable<T> whose elements are the result of invoking the one-to-many projection function collectionSelector on each element of source and then mapping each of those sequence elements and their corresponding source element to a result element.

例外

sourcecollectionSelectorresultSelectornullsource or collectionSelector or resultSelector is null.

示例

下面的代码示例演示如何使用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) 对数组执行一对多投影。The following code example demonstrates how to use SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) to perform a one-to-many projection over an array. 此示例使用结果选择器函数来保持源元素对应于最终调用范围内的每个中间序列 SelectThis example uses a result selector function to keep the source element that corresponds to each intermediate sequence in scope for the final call to Select.

class PetOwner
{
    public string Name { get; set; }
    public List<Pet> Pets { get; set; }
}

class Pet
{
    public string Name { get; set; }
    public string Breed { get; set; }
}

public static void SelectManyEx3()
{
    PetOwner[] petOwners =
        { new PetOwner { Name="Higa", 
              Pets = new List<Pet>{
                  new Pet { Name="Scruffy", Breed="Poodle" },
                  new Pet { Name="Sam", Breed="Hound" } } },
          new PetOwner { Name="Ashkenazi", 
              Pets = new List<Pet>{
                  new Pet { Name="Walker", Breed="Collie" },
                  new Pet { Name="Sugar", Breed="Poodle" } } },
          new PetOwner { Name="Price", 
              Pets = new List<Pet>{
                  new Pet { Name="Scratches", Breed="Dachshund" },
                  new Pet { Name="Diesel", Breed="Collie" } } },
          new PetOwner { Name="Hines", 
              Pets = new List<Pet>{
                  new Pet { Name="Dusty", Breed="Collie" } } }
        };

    // This query demonstrates how to obtain a sequence of
    // the names of all the pets whose breed is "Collie", while
    // keeping an association with the owner that owns the pet.
    var query =
        petOwners.AsQueryable()
        // Create a sequence of ALL the Pet objects. Then
        // project an anonymous type that consists of each
        // Pet in the new sequence and the PetOwner object
        // from the initial array that corresponds to that pet.
       .SelectMany(owner => owner.Pets,
                   (owner, pet) => new { owner, pet })
        // Filter the sequence of anonymous types to only
        // keep pets whose breed is "Collie".
        .Where(ownerAndPet => ownerAndPet.pet.Breed == "Collie")
        // Project an anonymous type that consists
        // of the pet owner's name and the pet's name.
        .Select(ownerAndPet => new
        {
            Owner = ownerAndPet.owner.Name,
            Pet = ownerAndPet.pet.Name
        });

    // Print the results.
    foreach (var obj in query)
        Console.WriteLine(obj);
}

/* This code produces the following output:

    { Owner = Ashkenazi, Pet = Walker }
    { Owner = Price, Pet = Diesel }
    { Owner = Hines, Pet = Dusty }
*/

Structure PetOwner
    Public Name As String
    Public Pets As List(Of Pet)
End Structure

Structure Pet
    Public Name As String
    Public Breed As String
End Structure

Shared Sub SelectManyEx3()
    Dim petOwners() As PetOwner = _
                {New PetOwner With {.Name = "Higa", _
                      .Pets = New List(Of Pet)(New Pet() { _
                          New Pet With {.Name = "Scruffy", .Breed = "Poodle"}, _
                          New Pet With {.Name = "Sam", .Breed = "Hound"}})}, _
                  New PetOwner With {.Name = "Ashkenazi", _
                      .Pets = New List(Of Pet)(New Pet() { _
                          New Pet With {.Name = "Walker", .Breed = "Collie"}, _
                          New Pet With {.Name = "Sugar", .Breed = "Poodle"}})}, _
                  New PetOwner With {.Name = "Price", _
                      .Pets = New List(Of Pet)(New Pet() { _
                          New Pet With {.Name = "Scratches", .Breed = "Dachshund"}, _
                          New Pet With {.Name = "Diesel", .Breed = "Collie"}})}, _
                  New PetOwner With {.Name = "Hines", _
                      .Pets = New List(Of Pet)(New Pet() { _
                          New Pet With {.Name = "Dusty", .Breed = "Collie"}})} _
                }

    ' This query demonstrates how to obtain a sequence of
    ' the names of all the pets whose breed is "Collie", while
    ' keeping an association with the owner that owns the pet.
    Dim query = petOwners.AsQueryable() _
        .SelectMany(Function(owner) owner.Pets, _
               Function(owner, pet) New With {owner, pet}) _
        .Where(Function(ownerAndPet) ownerAndPet.pet.Breed = "Collie") _
        .Select(Function(ownerAndPet) New With { _
            .Owner = ownerAndPet.owner.Name, _
            .Pet = ownerAndPet.pet.Name})

    Dim output As New System.Text.StringBuilder
    For Each obj In query
        output.AppendLine(String.Format("Owner={0}, Pet={1}", obj.Owner, obj.Pet))
    Next

    ' Display the output.
    MsgBox(output.ToString())
End Sub

' This code produces the following output:

' Owner=Ashkenazi, Pet=Walker
' Owner=Price, Pet=Diesel
' Owner=Hines, Pet=Dusty

注解

此方法至少具有一个类型 Expression<TDelegate> 的参数,其类型参数为 Func<T,TResult> 类型之一。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 对于这些参数,可以传入 lambda 表达式,并将其编译为 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) 方法生成一个 MethodCallExpression,它表示作为构造的泛型方法调用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) 本身。The SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) method generates a MethodCallExpression that represents calling SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) itself as a constructed generic method. 然后,它将 MethodCallExpression 传递到 IQueryProviderCreateQuery(Expression) 方法(由 source 参数的 Provider 属性表示)。It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

因执行表示调用 SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) 的表达式树而发生的查询行为取决于 source 参数类型的实现。The query behavior that occurs as a result of executing an expression tree that represents calling SelectMany<TSource,TCollection,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TCollection>>>, Expression<Func<TSource,TCollection,TResult>>) depends on the implementation of the type of the source parameter. 预期的行为是对 source 的每个元素调用 collectionSelector,以将其投影到可枚举的形式。The expected behavior is that it invokes collectionSelector on each element of source to project it into an enumerable form. 然后,对每个中间序列中的每个元素调用 resultSelector 所表示的函数。Then the function represented by resultSelector is invoked on each element in each intermediate sequence. 生成的值连接为一维序列。The resulting values are concatenated into a single, one-dimensional sequence.

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>)

将序列的每个元素投影到一个 IEnumerable<T>,并将结果序列组合为一个序列。Projects each element of a sequence to an IEnumerable<T> and combines the resulting sequences into one sequence. 每个源元素的索引用于该元素的投影表。The index of each source element is used in the projected form of that element.

public:
generic <typename TSource, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TResult> ^ SelectMany(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, int, System::Collections::Generic::IEnumerable<TResult> ^> ^> ^ selector);
public static System.Linq.IQueryable<TResult> SelectMany<TSource,TResult> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,int,System.Collections.Generic.IEnumerable<TResult>>> selector);
static member SelectMany : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, int, seq<'Result>>> -> System.Linq.IQueryable<'Result>
<Extension()>
Public Function SelectMany(Of TSource, TResult) (source As IQueryable(Of TSource), selector As Expression(Of Func(Of TSource, Integer, IEnumerable(Of TResult)))) As IQueryable(Of TResult)

类型参数

TSource

source 的元素类型。The type of the elements of source.

TResult

selector 表示的函数返回的序列中的元素的类型。The type of the elements of the sequence returned by the function represented by selector.

参数

source
IQueryable<TSource>

一个要投影的值序列。A sequence of values to project.

selector
Expression<Func<TSource,Int32,IEnumerable<TResult>>>

要应用于每个元素的投影函数;此函数的第二个参数表示源元素的索引。A projection function to apply to each element; the second parameter of this function represents the index of the source element.

返回

IQueryable<TResult>

一个 IQueryable<T>,其元素是对输入序列的每个元素调用一对多投影函数的结果。An IQueryable<T> whose elements are the result of invoking a one-to-many projection function on each element of the input sequence.

例外

sourceselectornullsource or selector is null.

示例

下面的代码示例演示如何使用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) 对数组执行一对多投影,并使用每个源元素的索引。The following code example demonstrates how to use SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) to perform a one-to-many projection over an array and use the index of each source element.

class PetOwner
{
    public string Name { get; set; }
    public List<string> Pets { get; set; }
}

public static void SelectManyEx2()
{
    PetOwner[] petOwners = 
        { new PetOwner { Name="Higa, Sidney", 
              Pets = new List<string>{ "Scruffy", "Sam" } },
          new PetOwner { Name="Ashkenazi, Ronen", 
              Pets = new List<string>{ "Walker", "Sugar" } },
          new PetOwner { Name="Price, Vernette", 
              Pets = new List<string>{ "Scratches", "Diesel" } },
          new PetOwner { Name="Hines, Patrick", 
              Pets = new List<string>{ "Dusty" } } };

    // For each PetOwner element in the source array,
    // project a sequence of strings where each string
    // consists of the index of the PetOwner element in the
    // source array and the name of each pet in PetOwner.Pets.
    IEnumerable<string> query =
        petOwners.AsQueryable()
        .SelectMany(
        (petOwner, index) => petOwner.Pets.Select(pet => index + pet)
        );

    foreach (string pet in query)
        Console.WriteLine(pet);
}

// This code produces the following output:
//
// 0Scruffy
// 0Sam
// 1Walker
// 1Sugar
// 2Scratches
// 2Diesel
// 3Dusty

Structure PetOwner
    Public Name As String
    Public Pets() As String
End Structure

Shared Sub SelectManyEx2()
    Dim petOwners() As PetOwner = _
        {New PetOwner With _
         {.Name = "Higa, Sidney", .Pets = New String() {"Scruffy", "Sam"}}, _
         New PetOwner With _
         {.Name = "Ashkenazi, Ronen", .Pets = New String() {"Walker", "Sugar"}}, _
         New PetOwner With _
         {.Name = "Price, Vernette", .Pets = New String() {"Scratches", "Diesel"}}, _
         New PetOwner With _
         {.Name = "Hines, Patrick", .Pets = New String() {"Dusty"}}}

    ' For each PetOwner element in the source array,
    ' project a sequence of strings where each string
    ' consists of the index of the PetOwner element in the
    ' source array and the name of each pet in PetOwner.Pets.
    Dim query As IEnumerable(Of String) = _
        petOwners.AsQueryable() _
        .SelectMany(Function(petOwner, index) petOwner.Pets.Select(Function(pet) index.ToString() + pet))

    Dim output As New System.Text.StringBuilder
    For Each pet As String In query
        output.AppendLine(pet)
    Next

    ' Display the output.
    MsgBox(output.ToString())
End Sub

' This code produces the following output:
'
' 0Scruffy
' 0Sam
' 1Walker
' 1Sugar
' 2Scratches
' 2Diesel
' 3Dusty

注解

此方法至少具有一个类型 Expression<TDelegate> 的参数,其类型参数为 Func<T,TResult> 类型之一。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 对于这些参数,可以传入 lambda 表达式,并将其编译为 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) 方法生成一个 MethodCallExpression,它表示作为构造的泛型方法调用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) 本身。The SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) method generates a MethodCallExpression that represents calling SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) itself as a constructed generic method. 然后,它将 MethodCallExpression 传递到 IQueryProviderCreateQuery(Expression) 方法(由 source 参数的 Provider 属性表示)。It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

因执行表示调用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) 的表达式树而发生的查询行为取决于 source 参数类型的实现。The query behavior that occurs as a result of executing an expression tree that represents calling SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,Int32,IEnumerable<TResult>>>) depends on the implementation of the type of the source parameter. 预期的行为是对 source 的每个元素调用 selector,以将其投影到可枚举的形式。The expected behavior is that it invokes selector on each element of source to project it into an enumerable form. 每个可枚举的结果都包含源元素的索引。Each enumerable result incorporates the index of the source element. 然后,它将可枚举的结果连接到单个一维序列。It then concatenates the enumerable results into a single, one-dimensional sequence.

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>)

将序列的每个元素投影到一个 IEnumerable<T>,并将结果序列组合为一个序列。Projects each element of a sequence to an IEnumerable<T> and combines the resulting sequences into one sequence.

public:
generic <typename TSource, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TResult> ^ SelectMany(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, System::Collections::Generic::IEnumerable<TResult> ^> ^> ^ selector);
public static System.Linq.IQueryable<TResult> SelectMany<TSource,TResult> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,System.Collections.Generic.IEnumerable<TResult>>> selector);
static member SelectMany : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, seq<'Result>>> -> System.Linq.IQueryable<'Result>
<Extension()>
Public Function SelectMany(Of TSource, TResult) (source As IQueryable(Of TSource), selector As Expression(Of Func(Of TSource, IEnumerable(Of TResult)))) As IQueryable(Of TResult)

类型参数

TSource

source 的元素类型。The type of the elements of source.

TResult

selector 表示的函数返回的序列中的元素的类型。The type of the elements of the sequence returned by the function represented by selector.

参数

source
IQueryable<TSource>

一个要投影的值序列。A sequence of values to project.

selector
Expression<Func<TSource,IEnumerable<TResult>>>

要应用于每个元素的投影函数。A projection function to apply to each element.

返回

IQueryable<TResult>

一个 IQueryable<T>,其元素是对输入序列的每个元素调用一对多投影函数的结果。An IQueryable<T> whose elements are the result of invoking a one-to-many projection function on each element of the input sequence.

例外

sourceselectornullsource or selector is null.

示例

下面的代码示例演示如何使用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) 对数组执行一对多投影。The following code example demonstrates how to use SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) to perform a one-to-many projection over an array.

class PetOwner
{
    public string Name { get; set; }
    public List<String> Pets { get; set; }
}

public static void SelectManyEx1()
{
    PetOwner[] petOwners = 
        { new PetOwner { Name="Higa, Sidney", 
              Pets = new List<string>{ "Scruffy", "Sam" } },
          new PetOwner { Name="Ashkenazi, Ronen", 
              Pets = new List<string>{ "Walker", "Sugar" } },
          new PetOwner { Name="Price, Vernette", 
              Pets = new List<string>{ "Scratches", "Diesel" } } };

    // Query using SelectMany().
    IEnumerable<string> query1 =
        petOwners.AsQueryable().SelectMany(petOwner => petOwner.Pets);

    Console.WriteLine("Using SelectMany():");

    // Only one foreach loop is required to iterate through the
    // results because it is a one-dimensional collection.
    foreach (string pet in query1)
        Console.WriteLine(pet);

    // This code shows how to use Select() instead of SelectMany().
    IEnumerable<List<String>> query2 =
        petOwners.AsQueryable().Select(petOwner => petOwner.Pets);

    Console.WriteLine("\nUsing Select():");

    // Notice that two foreach loops are required to iterate through
    // the results because the query returns a collection of arrays.
    foreach (List<String> petList in query2)
    {
        foreach (string pet in petList)
        {
            Console.WriteLine(pet);
        }
        Console.WriteLine();
    }
}

/*
    This code produces the following output:

    Using SelectMany():
    Scruffy
    Sam
    Walker
    Sugar
    Scratches
    Diesel

    Using Select():
    Scruffy
    Sam

    Walker
    Sugar

    Scratches
    Diesel
*/

Structure PetOwner
    Public Name As String
    Public Pets() As String
End Structure

Shared Sub SelectManyEx1()
    Dim petOwners() As PetOwner = _
        {New PetOwner With _
         {.Name = "Higa, Sidney", .Pets = New String() {"Scruffy", "Sam"}}, _
         New PetOwner With _
         {.Name = "Ashkenazi, Ronen", .Pets = New String() {"Walker", "Sugar"}}, _
         New PetOwner With _
         {.Name = "Price, Vernette", .Pets = New String() {"Scratches", "Diesel"}}}

    ' Query using SelectMany().
    Dim query1 As IEnumerable(Of String) = _
                petOwners.AsQueryable().SelectMany(Function(petOwner) petOwner.Pets)

    Dim output As New System.Text.StringBuilder("Using SelectMany():" & vbCrLf)
    ' Only one foreach loop is required to iterate through 
    ' the results because it is a one-dimensional collection.
    For Each pet As String In query1
        output.AppendLine(pet)
    Next

    ' This code shows how to use Select() instead of SelectMany().
    Dim query2 As IEnumerable(Of String()) = _
                petOwners.AsQueryable().Select(Function(petOwner) petOwner.Pets)

    output.AppendLine(vbCrLf & "Using Select():")
    ' Notice that two foreach loops are required to iterate through 
    ' the results because the query returns a collection of arrays.
    For Each petArray() As String In query2
        For Each pet As String In petArray
            output.AppendLine(pet)
        Next
    Next

    ' Display the output.
    MsgBox(output.ToString())
End Sub

' This code produces the following output:

' Using SelectMany():
' Scruffy
' Sam
' Walker
' Sugar
' Scratches
' Diesel

' Using Select():
' Scruffy
' Sam
' Walker
' Sugar
' Scratches
' Diesel

注解

此方法至少具有一个类型 Expression<TDelegate> 的参数,其类型参数为 Func<T,TResult> 类型之一。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 对于这些参数,可以传入 lambda 表达式,并将其编译为 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) 方法生成一个 MethodCallExpression,它表示作为构造的泛型方法调用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) 本身。The SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) method generates a MethodCallExpression that represents calling SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) itself as a constructed generic method. 然后,它将 MethodCallExpression 传递到 IQueryProviderCreateQuery(Expression) 方法(由 source 参数的 Provider 属性表示)。It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

因执行表示调用 SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) 的表达式树而发生的查询行为取决于 source 参数类型的实现。The query behavior that occurs as a result of executing an expression tree that represents calling SelectMany<TSource,TResult>(IQueryable<TSource>, Expression<Func<TSource,IEnumerable<TResult>>>) depends on the implementation of the type of the source parameter. 预期的行为是对 source 的每个元素调用 selector,以将其投影到可枚举的形式。The expected behavior is that it invokes selector on each element of source to project it into an enumerable form. 然后,它将可枚举的结果连接到单个一维序列。It then concatenates the enumerable results into a single, one-dimensional sequence.

适用于