Data is not always clean. Depending on how it is produced a number might be rendered in the JSON body as a true JSON number, e.g. 5, but it might also be rendered as a string, e.g. "5". Alternatively, a number that should be an integer might instead be rendered as a floating point, e.g. 5.0, or even "5.0".

Coercion attempts to clean up dirty values to fit the datatype of a field. For instance:

For instance:

PUT my_index
{
  "mappings": {
    "properties": {
      "number_one": {
        "type": "integer"
      },
      "number_two": {
        "type": "integer",
        "coerce": false
      }
    }
  }
}

PUT my_index/_doc/1
{
  "number_one": "10" 
}

PUT my_index/_doc/2
{
  "number_two": "10" 
}

The coerce setting is allowed to have different settings for fields of the same name in the same index. Its value can be updated on existing fields using the PUT mapping API.

PUT my_index
{
  "settings": {
    "index.mapping.coerce": false
  },
  "mappings": {
    "properties": {
      "number_one": {
        "type": "integer",
        "coerce": true
      },
      "number_two": {
        "type": "integer"
      }
    }
  }
}

PUT my_index/_doc/1
{ "number_one": "10" } 

PUT my_index/_doc/2
{ "number_two": "10" }