Arrays [array]

In Elasticsearch, there is no dedicated array data type. Any field can contain zero or more values by default, however, all values in the array must be of the same data type. For instance:

• an array of strings: [ "one", "two" ]
• an array of integers: [ 1, 2 ]
• an array of arrays: [ 1, [ 2, 3 ]] which is the equivalent of [ 1, 2, 3 ]
• an array of objects: [ { "name": "Mary", "age": 12 }, { "name": "John", "age": 10 }]

::::{admonition} Arrays with object field type vs nested type :class: note

Arrays of objects in Elasticsearch do not behave as you would expect: queries may match fields across different objects in the array, leading to unexpected results. By default, arrays of objects are flattened during indexing. To ensure queries match values within the same object, use the nested data type instead of the object data type.

This behavior is explained in more detail in nested.

::::

When adding a field dynamically, the first value in the array determines the field type. All subsequent values must be of the same data type or it must at least be possible to coerce subsequent values to the same data type.

Arrays with a mixture of data types are not supported: [ 10, "some string" ]

An array may contain null values, which are either replaced by the configured null_value or skipped entirely. An empty array [] is treated as a missing field — a field with no values.

Nothing needs to be pre-configured in order to use arrays in documents, they are supported out of the box:

PUT my-index-000001/_doc/1
{
  "message": "some arrays in this document...",
  "tags":  [ "elasticsearch", "wow" ], <1>
  "lists": [ <2>
    {
      "name": "prog_list",
      "description": "programming list"
    },
    {
      "name": "cool_list",
      "description": "cool stuff list"
    }
  ]
}

PUT my-index-000001/_doc/2 <3>
{
  "message": "no arrays in this document...",
  "tags":  "elasticsearch",
  "lists": {
    "name": "prog_list",
    "description": "programming list"
  }
}

GET my-index-000001/_search
{
  "query": {
    "match": {
      "tags": "elasticsearch" <4>
    }
  }
}

1. The tags field is dynamically added as a string field.
2. The lists field is dynamically added as an object field.
3. The second document contains no arrays, but can be indexed into the same fields.
4. The query looks for elasticsearch in the tags field, and matches both documents.

::::{tip} You can modify arrays using the update API.

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