Upload data to Azure Search using the .NET SDK

This article will show you how to use the Azure Search .NET SDK to import data into an Azure Search index.

Before beginning this walkthrough, you should already have created an Azure Search index. This article also assumes that you have already created a SearchServiceClient object, as shown in Create an Azure Search index using the .NET SDK.


All sample code in this article is written in C#. You can find the full source code on GitHub. You can also read about the Azure Search .NET SDK for a more detailed walk through of the sample code.

In order to push documents into your index using the .NET SDK, you will need to:

  1. Create a SearchIndexClient object to connect to your search index.
  2. Create an IndexBatch containing the documents to be added, modified, or deleted.
  3. Call the Documents.Index method of your SearchIndexClient to send the IndexBatch to your search index.

Create an instance of the SearchIndexClient class

To import data into your index using the Azure Search .NET SDK, you will need to create an instance of the SearchIndexClient class. You can construct this instance yourself, but it's easier if you already have a SearchServiceClient instance to call its Indexes.GetClient method. For example, here is how you would obtain a SearchIndexClient for the index named "hotels" from a SearchServiceClient named serviceClient:

ISearchIndexClient indexClient = serviceClient.Indexes.GetClient("hotels");


In a typical search application, index management and population is handled by a separate component from search queries. Indexes.GetClient is convenient for populating an index because it saves you the trouble of providing another SearchCredentials. It does this by passing the admin key that you used to create the SearchServiceClient to the new SearchIndexClient. However, in the part of your application that executes queries, it is better to create the SearchIndexClient directly so that you can pass in a query key instead of an admin key. This is consistent with the principle of least privilege and will help to make your application more secure. You can find out more about admin keys and query keys in the Azure Search REST API reference.

SearchIndexClient has a Documents property. This property provides all the methods you need to add, modify, delete, or query documents in your index.

Decide which indexing action to use

To import data using the .NET SDK, you will need to package up your data into an IndexBatch object. An IndexBatch encapsulates a collection of IndexAction objects, each of which contains a document and a property that tells Azure Search what action to perform on that document (upload, merge, delete, etc). Depending on which of the below actions you choose, only certain fields must be included for each document:

Action Description Necessary fields for each document Notes
Upload An Upload action is similar to an "upsert" where the document will be inserted if it is new and updated/replaced if it exists. key, plus any other fields you wish to define When updating/replacing an existing document, any field that is not specified in the request will have its field set to null. This occurs even when the field was previously set to a non-null value.
Merge Updates an existing document with the specified fields. If the document does not exist in the index, the merge will fail. key, plus any other fields you wish to define Any field you specify in a merge will replace the existing field in the document. This includes fields of type DataType.Collection(DataType.String). For example, if the document contains a field tags with value ["budget"] and you execute a merge with value ["economy", "pool"] for tags, the final value of the tags field will be ["economy", "pool"]. It will not be ["budget", "economy", "pool"].
MergeOrUpload This action behaves like Merge if a document with the given key already exists in the index. If the document does not exist, it behaves like Upload with a new document. key, plus any other fields you wish to define -
Delete Removes the specified document from the index. key only Any fields you specify other than the key field will be ignored. If you want to remove an individual field from a document, use Merge instead and simply set the field explicitly to null.

You can specify what action you want to use with the various static methods of the IndexBatch and IndexAction classes, as shown in the next section.

Construct your IndexBatch

Now that you know which actions to perform on your documents, you are ready to construct the IndexBatch. The example below shows how to create a batch with a few different actions. Note that our example uses a custom class called Hotel that maps to a document in the "hotels" index.

var actions =
    new IndexAction<Hotel>[]
            new Hotel()
                HotelId = "1",
                BaseRate = 199.0,
                Description = "Best hotel in town",
                DescriptionFr = "Meilleur hôtel en ville",
                HotelName = "Fancy Stay",
                Category = "Luxury",
                Tags = new[] { "pool", "view", "wifi", "concierge" },
                ParkingIncluded = false,
                SmokingAllowed = false,
                LastRenovationDate = new DateTimeOffset(2010, 6, 27, 0, 0, 0, TimeSpan.Zero),
                Rating = 5,
                Location = GeographyPoint.Create(47.678581, -122.131577)
            new Hotel()
                HotelId = "2",
                BaseRate = 79.99,
                Description = "Cheapest hotel in town",
                DescriptionFr = "Hôtel le moins cher en ville",
                HotelName = "Roach Motel",
                Category = "Budget",
                Tags = new[] { "motel", "budget" },
                ParkingIncluded = true,
                SmokingAllowed = true,
                LastRenovationDate = new DateTimeOffset(1982, 4, 28, 0, 0, 0, TimeSpan.Zero),
                Rating = 1,
                Location = GeographyPoint.Create(49.678581, -122.131577)
            new Hotel()
                HotelId = "3",
                BaseRate = 129.99,
                Description = "Close to town hall and the river"
        IndexAction.Delete(new Hotel() { HotelId = "6" })

var batch = IndexBatch.New(actions);

In this case, we are using Upload, MergeOrUpload, and Delete as our search actions, as specified by the methods called on the IndexAction class.

Assume that this example "hotels" index is already populated with a number of documents. Note how we did not have to specify all the possible document fields when using MergeOrUpload and how we only specified the document key (HotelId) when using Delete.

Also, note that you can only include up to 1000 documents in a single indexing request.


In this example, we are applying different actions to different documents. If you wanted to perform the same actions across all documents in the batch, instead of calling IndexBatch.New, you could use the other static methods of IndexBatch. For example, you could create batches by calling IndexBatch.Merge, IndexBatch.MergeOrUpload, or IndexBatch.Delete. These methods take a collection of documents (objects of type Hotel in this example) instead of IndexAction objects.

Import data to the index

Now that you have an initialized IndexBatch object, you can send it to the index by calling Documents.Index on your SearchIndexClient object. The following example shows how to call Index, as well as some extra steps you will need to perform:

catch (IndexBatchException e)
    // Sometimes when your Search service is under load, indexing will fail for some of the documents in
    // the batch. Depending on your application, you can take compensating actions like delaying and
    // retrying. For this simple demo, we just log the failed document keys and continue.
        "Failed to index some of the documents: {0}",
        String.Join(", ", e.IndexingResults.Where(r => !r.Succeeded).Select(r => r.Key)));

Console.WriteLine("Waiting for documents to be indexed...\n");

Note the try/catch surrounding the call to the Index method. The catch block handles an important error case for indexing. If your Azure Search service fails to index some of the documents in the batch, an IndexBatchException is thrown by Documents.Index. This can happen if you are indexing documents while your service is under heavy load. We strongly recommend explicitly handling this case in your code. You can delay and then retry indexing the documents that failed, or you can log and continue like the sample does, or you can do something else depending on your application's data consistency requirements.

Finally, the code in the example above delays for two seconds. Indexing happens asynchronously in your Azure Search service, so the sample application needs to wait a short time to ensure that the documents are available for searching. Delays like this are typically only necessary in demos, tests, and sample applications.

How the .NET SDK handles documents

You may be wondering how the Azure Search .NET SDK is able to upload instances of a user-defined class like Hotel to the index. To help answer that question, let's look at the Hotel class, which maps to the index schema defined in Create an Azure Search index using the .NET SDK:

public partial class Hotel
    public string HotelId { get; set; }

    [IsFilterable, IsSortable, IsFacetable]
    public double? BaseRate { get; set; }

    public string Description { get; set; }

    public string DescriptionFr { get; set; }

    [IsSearchable, IsFilterable, IsSortable]
    public string HotelName { get; set; }

    [IsSearchable, IsFilterable, IsSortable, IsFacetable]
    public string Category { get; set; }

    [IsSearchable, IsFilterable, IsFacetable]
    public string[] Tags { get; set; }

    [IsFilterable, IsFacetable]
    public bool? ParkingIncluded { get; set; }

    [IsFilterable, IsFacetable]
    public bool? SmokingAllowed { get; set; }

    [IsFilterable, IsSortable, IsFacetable]
    public DateTimeOffset? LastRenovationDate { get; set; }

    [IsFilterable, IsSortable, IsFacetable]
    public int? Rating { get; set; }

    [IsFilterable, IsSortable]
    public GeographyPoint Location { get; set; }

    // ToString() method omitted for brevity...

The first thing to notice is that each public property of Hotel corresponds to a field in the index definition, but with one crucial difference: The name of each field starts with a lower-case letter ("camel case"), while the name of each public property of Hotel starts with an upper-case letter ("Pascal case"). This is a common scenario in .NET applications that perform data-binding where the target schema is outside the control of the application developer. Rather than having to violate the .NET naming guidelines by making property names camel-case, you can tell the SDK to map the property names to camel-case automatically with the [SerializePropertyNamesAsCamelCase] attribute.


The Azure Search .NET SDK uses the NewtonSoft JSON.NET library to serialize and deserialize your custom model objects to and from JSON. You can customize this serialization if needed. You can find more details in Custom Serialization with JSON.NET. One example of this is the use of the [JsonProperty] attribute on the DescriptionFr property in the sample code above.

The second important thing about the Hotel class are the data types of the public properties. The .NET types of these properties map to their equivalent field types in the index definition. For example, the Category string property maps to the category field, which is of type DataType.String. There are similar type mappings between bool? and DataType.Boolean, DateTimeOffset? and DataType.DateTimeOffset, and so forth. The specific rules for the type mapping are documented with the Documents.Get method in the Azure Search .NET SDK reference.

This ability to use your own classes as documents works in both directions; You can also retrieve search results and have the SDK automatically deserialize them to a type of your choice, as shown in the next article.


The Azure Search .NET SDK also supports dynamically-typed documents using the Document class, which is a key/value mapping of field names to field values. This is useful in scenarios where you don't know the index schema at design-time, or where it would be inconvenient to bind to specific model classes. All the methods in the SDK that deal with documents have overloads that work with the Document class, as well as strongly-typed overloads that take a generic type parameter. Only the latter are used in the sample code in this article.

Why you should use nullable data types

When designing your own model classes to map to an Azure Search index, we recommend declaring properties of value types such as bool and int to be nullable (for example, bool? instead of bool). If you use a non-nullable property, you have to guarantee that no documents in your index contain a null value for the corresponding field. Neither the SDK nor the Azure Search service will help you to enforce this.

This is not just a hypothetical concern: Imagine a scenario where you add a new field to an existing index that is of type DataType.Int32. After updating the index definition, all documents will have a null value for that new field (since all types are nullable in Azure Search). If you then use a model class with a non-nullable int property for that field, you will get a JsonSerializationException like this when trying to retrieve documents:

Error converting value {null} to type 'System.Int32'. Path 'IntValue'.

For this reason, we recommend that you use nullable types in your model classes as a best practice.

Next steps

After populating your Azure Search index, you will be ready to start issuing queries to search for documents. See Query Your Azure Search Index for details.