Arrays of inner object fields do not work the way you may expect. Lucene has no concept of inner objects, so Elasticsearch flattens object hierarchies into a simple list of field names and values. For instance, the following document:

PUT my_index/_doc/1
{
  "group" : "fans",
  "user" : [ 
    {
      "first" : "John",
      "last" :  "Smith"
    },
    {
      "first" : "Alice",
      "last" :  "White"
    }
  ]
}

would be transformed internally into a document that looks more like this:

{
  "group" :        "fans",
  "user.first" : [ "alice", "john" ],
  "user.last" :  [ "smith", "white" ]
}

The user.first and user.last fields are flattened into multi-value fields, and the association between alice and white is lost. This document would incorrectly match a query for alice AND smith:

GET my_index/_search
{
  "query": {
    "bool": {
      "must": [
        { "match": { "user.first": "Alice" }},
        { "match": { "user.last":  "Smith" }}
      ]
    }
  }
}

If you need to index arrays of objects and to maintain the independence of each object in the array, you should use the nested datatype instead of the object datatype. Internally, nested objects index each object in the array as a separate hidden document, meaning that each nested object can be queried independently of the others, with the nested query:

PUT my_index
{
  "mappings": {
    "properties": {
      "user": {
        "type": "nested" 
      }
    }
  }
}

PUT my_index/_doc/1
{
  "group" : "fans",
  "user" : [
    {
      "first" : "John",
      "last" :  "Smith"
    },
    {
      "first" : "Alice",
      "last" :  "White"
    }
  ]
}

GET my_index/_search
{
  "query": {
    "nested": {
      "path": "user",
      "query": {
        "bool": {
          "must": [
            { "match": { "user.first": "Alice" }},
            { "match": { "user.last":  "Smith" }} 
          ]
        }
      }
    }
  }
}

GET my_index/_search
{
  "query": {
    "nested": {
      "path": "user",
      "query": {
        "bool": {
          "must": [
            { "match": { "user.first": "Alice" }},
            { "match": { "user.last":  "White" }} 
          ]
        }
      },
      "inner_hits": { 
        "highlight": {
          "fields": {
            "user.first": {}
          }
        }
      }
    }
  }
}

Nested documents can be:

The following parameters are accepted by nested fields:

Because nested documents are indexed as separate documents, they can only be accessed within the scope of the nested query, the nested/reverse_nested aggregations, or nested inner hits.

For instance, if a string field within a nested document has index_options set to offsets to allow use of the postings during the highlighting, these offsets will not be available during the main highlighting phase. Instead, highlighting needs to be performed via nested inner hits.

Indexing a document with 100 nested fields actually indexes 101 documents as each nested document is indexed as a separate document. To safeguard against ill-defined mappings the number of nested fields that can be defined per index has been limited to 50. See Settings to prevent mappings explosion.

Indexing a document with an array of 100 objects within a nested field, will actually create 101 documents, as each nested object will be indexed as a separate document. To prevent out of memory errors when a single document contains too many nested json objects, the number of nested json objects that a single document may contain across all fields has been limited to 10000. See Settings to prevent mappings explosion.