ObjectQuery<T>.GroupBy(String, String, ObjectParameter[]) Method

Определение

Группирует результаты запроса по заданному критерию. Groups the query results by the specified criteria.

public System.Data.Objects.ObjectQuery<System.Data.Common.DbDataRecord> GroupBy (string keys, string projection, params System.Data.Objects.ObjectParameter[] parameters);
Параметры
keys
String

Ключевые столбцы, по которым группируются результаты. The key columns by which to group the results.

projection
String

Список выбранных свойств, определяющий проекцию. The list of selected properties that defines the projection.

parameters
ObjectParameter[]

Параметры (ноль или более), используемые в этом методе. Zero or more parameters that are used in this method.

Возвраты

Новый экземпляр запроса ObjectQuery<T> типа DbDataRecord, эквивалентный первоначальному экземпляру с примененным к нему предложением GROUP BY. A new ObjectQuery<T> instance of type DbDataRecord that is equivalent to the original instance with GROUP BY applied.

Исключения

Параметр query имеет значение null или является пустой строкой. The query parameter is null or an empty string. - или - -or- Параметр projection имеет значение null или является пустой строкой. The projection parameter is null or an empty string.

Примеры

Этот пример основан на модели AdventureWorks Sales.This example is based on the AdventureWorks Sales Model.

В данном примере создается новый объект ObjectQuery<T>, содержащий результаты существующего запроса, сгруппированные по названиям продуктов.This example creates a new ObjectQuery<T> object that contains the results of the existing query grouped by product name.

    using (AdventureWorksEntities context =
        new AdventureWorksEntities())
    {
        string queryString = @"SELECT VALUE product 
            FROM AdventureWorksEntities.Products AS product";

        ObjectQuery<Product> productQuery =
            new ObjectQuery<Product>(queryString,
                context, MergeOption.NoTracking);

        ObjectQuery<DbDataRecord> productQuery2 =
            productQuery.GroupBy("it.name AS pn",
            "Sqlserver.COUNT(it.Name) as count, pn");

        // Iterate through the collection of Products
        // after the GroupBy method was called.
        foreach (DbDataRecord result in productQuery2)
        {
            Console.WriteLine("Name: {0}; Count: {1}",
                result["pn"], result["count"]);
        }
    }
}
    Using context As New AdventureWorksEntities()
        Dim queryString As String = "SELECT VALUE product " & vbCr & vbLf & " FROM AdventureWorksEntities.Products AS product"

        Dim productQuery As New ObjectQuery(Of Product)(queryString, context, MergeOption.NoTracking)

        Dim productQuery2 As ObjectQuery(Of DbDataRecord) = _
            productQuery.GroupBy("it.name AS pn", "Sqlserver.COUNT(it.Name) as count, pn")

        ' Iterate through the collection of Products 
        ' after the GroupBy method was called. 
        For Each result As DbDataRecord In productQuery2
            Console.WriteLine("Name: {0}; Count: {1}", result("pn"), result("count"))
        Next
    End Using
End Sub

Этот пример возвращает набор вложенных записей, содержащих Contact.LastName столбцов, сгруппированных и отсортированных в алфавитном порядке по первой букве Contact.LastName.This example returns a set of nested data records that contain the Contact.LastName column, grouped and sorted alphabetically by the first letter of Contact.LastName.

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
{
    // Define the query with a GROUP BY clause that returns
    // a set of nested LastName records grouped by first letter.
    ObjectQuery<DbDataRecord> query =
        context.Contacts
        .GroupBy("SUBSTRING(it.LastName, 1, 1) AS ln", "ln")
        .Select("it.ln AS ln, (SELECT c1.LastName " +
        "FROM AdventureWorksEntities.Contacts AS c1 " +
        "WHERE SubString(c1.LastName, 1, 1) = it.ln) AS CONTACT")
        .OrderBy("it.ln");

    // Execute the query and walk through the nested records.
    foreach (DbDataRecord rec in
        query.Execute(MergeOption.AppendOnly))
    {
        Console.WriteLine("Last names that start with the letter '{0}':",
                    rec[0]);
        List<DbDataRecord> list = rec[1] as List<DbDataRecord>;
        foreach (DbDataRecord r in list)
        {
            for (int i = 0; i < r.FieldCount; i++)
            {
                Console.WriteLine("   {0} ", r[i]);
            }
        }
    }
}
Using context As New AdventureWorksEntities()
    ' Define the query with a GROUP BY clause that returns 
    ' a set of nested LastName records grouped by first letter. 
    Dim query As ObjectQuery(Of DbDataRecord) = _
        context.Contacts.GroupBy("SUBSTRING(it.LastName, 1, 1) AS ln", "ln") _
        .Select("it.ln AS ln, (SELECT c1.LastName FROM AdventureWorksEntities.Contacts AS c1 " & _
                "WHERE SubString(c1.LastName, 1, 1) = it.ln) AS CONTACT").OrderBy("it.ln")

    ' Execute the query and walk through the nested records. 
    For Each rec As DbDataRecord In query.Execute(MergeOption.AppendOnly)
        Console.WriteLine("Last names that start with the letter '{0}':", rec(0))
        Dim list As List(Of DbDataRecord) = TryCast(rec(1), List(Of DbDataRecord))
        For Each r As DbDataRecord In list
            For i As Integer = 0 To r.FieldCount - 1
                Console.WriteLine(" {0} ", r(i))
            Next
        Next
    Next
End Using

Комментарии

GroupBy применяет проекцию, заданную по projection параметр.GroupBy applies the projection specified by the projection parameter. Это означает, что свойство ObjectQuery<T>, возвращаемое методом GroupBy, всегда будет иметь тип DbDataRecord.This means that the ObjectQuery<T> returned by the GroupBy method is always of type DbDataRecord. Дополнительные сведения см. в разделе запросы объектов.For more information, see Object Queries.

Применяется к