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OData $select syntax in Azure Cognitive Search

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You can use the OData $select parameter to choose which fields to include in search results from Azure Cognitive Search. This article describes the syntax of $select in detail. For more general information about how to use $select when presenting search results, see How to work with search results in Azure Cognitive Search.

Syntax

The $select parameter determines which fields for each document are returned in the query result set. The following EBNF (Extended Backus-Naur Form) defines the grammar for the $select parameter:

select_expression ::= '*' | field_path(',' field_path)*

field_path ::= identifier('/'identifier)*

An interactive syntax diagram is also available:

OData syntax diagram for Azure Cognitive Search

Note

See OData expression syntax reference for Azure Cognitive Search for the complete EBNF.

The $select parameter comes in two forms:

  1. A single star (*), indicating that all retrievable fields should be returned, or
  2. A comma-separated list of field paths, identifying which fields should be returned.

When using the second form, you may only specify retrievable fields in the list.

If you list a complex field without specifying its sub-fields explicitly, all retrievable sub-fields will be included in the query result set. For example, assume your index has an Address field with Street, City, and Country sub-fields that are all retrievable. If you specify Address in $select, the query results will include all three sub-fields.

Examples

Include the HotelId, HotelName, and Rating top-level fields in the results, as well as the City sub-field of Address:

    $select=HotelId, HotelName, Rating, Address/City

An example result might look like this:

{
  "HotelId": "1",
  "HotelName": "Secret Point Motel",
  "Rating": 4,
  "Address": {
    "City": "New York"
  }
}

Include the HotelName top-level field in the results, as well as all sub-fields of Address, and the Type and BaseRate sub-fields of each object in the Rooms collection:

    $select=HotelName, Address, Rooms/Type, Rooms/BaseRate

An example result might look like this:

{
  "HotelName": "Secret Point Motel",
  "Rating": 4,
  "Address": {
    "StreetAddress": "677 5th Ave",
    "City": "New York",
    "StateProvince": "NY",
    "Country": "USA",
    "PostalCode": "10022"
  },
  "Rooms": [
    {
      "Type": "Budget Room",
      "BaseRate": 9.69
    },
    {
      "Type": "Budget Room",
      "BaseRate": 8.09
    }
  ]
}

Next steps