Spring Data Elasticsearch Object Mapping is the process that maps a Java object - the domain entity - into the JSON representation that is stored in Elasticsearch and back.
Earlier versions of Spring Data Elasticsearch used a Jackson based conversion, Spring Data Elasticsearch 3.2.x introduced the <<elasticsearch.mapping.meta-model>>.
As of version 4.0 only the Meta Object Mapping is used, the Jackson based mapper is not available anymore and the `MappingElasticsearchConverter` is used.
* `@Field`: Applied at the field level and defines properties of the field, most of the attributes map to the respective https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping.html[Elasticsearch Mapping] definitions (the following list is not complete, check the annotation Javadoc for a complete reference):
Properties that derive from `TemporalAccessor` or are of type `java.util.Date` must either have a `@Field` annotation
of type `FieldType.Date` or a custom converter must be registered for this type. This paragraph describes the use of
`FieldType.Date`.
There are two attributes of the `@Field` annotation that define which date format information is written to the
mapping (also see https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-date-format.html#built-in-date-formats[Elasticsearch Built In Formats] and https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-date-format.html#custom-date-formats[Elasticsearch Custom Date Formats])
The `format` attributes is used to define at least one of the predefined formats. If it is not defined, then a
default value of __date_optional_time_ and _epoch_millis_ is used.
The `pattern` attribute can be used to add additional custom format strings. If you want to use only custom date formats, you must set the `format` property to empty `{}`.
The following table shows the different attributes and the mapping created from their values:
NOTE: If you are using a custom date format, you need to use _uuuu_ for the year instead of _yyyy_.
This is due to a https://www.elastic.co/guide/en/elasticsearch/reference/current/migrate-to-java-time.html#java-time-migration-incompatible-date-formats[change in Elasticsearch 7].
Without further configuration, Spring Data Elasticsearch will use the property name of an object as field name in Elasticsearch. This can be changed for individual field by using the `@Field` annotation on that property.
It is also possible to define a `FieldNamingStrategy` in the configuration of the client (<<elasticsearch.clients>>). If for example a `SnakeCaseFieldNamingStrategy` is configured, the property _sampleProperty_ of the object would be mapped to _sample_property_ in Elasticsearch. A `FieldNamingStrategy` applies to all entities; it can be overwritten by
setting a specific name with `@Field` on a property.
NOTE: Make sure to add types with `@TypeAlias` to the initial entity set (`AbstractElasticsearchConfiguration#getInitialEntitySet`) to already have entity information available when first reading data from the store.
NOTE: Type hints will not be written for nested Objects unless the properties type is `Object`, an interface or the actual value type does not match the properties declaration.
Spring Data Elasticsearch supports the GeoJson types by providing an interface `GeoJson` and implementations for the different geometries.
They are mapped to Elasticsearch documents according to the GeoJson specification.
The corresponding properties of the entity are specified in the index mappings as `geo_shape` when the index mappings is written. (check the https://www.elastic.co/guide/en/elasticsearch/reference/current/geo-shape.html[Elasticsearch documentation] as well)
For values inside Collections apply the same mapping rules as for aggregate roots when it comes to _type hints_ and <<elasticsearch.mapping.meta-model.conversions>>.
For values inside Maps apply the same mapping rules as for aggregate roots when it comes to _type hints_ and <<elasticsearch.mapping.meta-model.conversions>>.
Looking at the `Configuration` from the <<elasticsearch.mapping.meta-model, previous section>> `ElasticsearchCustomConversions` allows registering specific rules for mapping domain and simple types.
