In Elasticsearch, a field mapping defines the characteristics of a field in an index, such as its data type, indexing options, and analysis settings. Field mappings are used to control how the data is indexed and searched in Elasticsearch, and they can be customized to fit the specific needs of the data being indexed.
When a new index is created in Elasticsearch, a default mapping is automatically generated based on the data types of the fields in the indexed documents. However, it’s often necessary to customize the mapping to achieve more specific indexing and search behavior.
Some of the characteristics that can be defined in a field mapping include:
1. Data type: Specifies the data type of the field, such as string, integer, or date.
2. Indexing options: Specifies how the field should be indexed, such as whether it should be analyzed for full-text search or not.
3. Analysis settings: Specifies how text fields should be analyzed and tokenized during indexing, such as which analyzer to use and which token filters to apply.
4. Multi-fields: Allows for multiple mappings to be defined for a single field, such as one for full-text search and another for exact matching.
5. Coerce: Allows for automatic conversion of data types, such as converting a string to a date.
6. Ignore above: Allows for the exclusion of certain parts of a field during indexing and search, such as excluding the first few characters of a string.
Field mappings can be defined explicitly in Elasticsearch using the PUT mapping API, or they can be generated automatically using dynamic mapping. Dynamic mapping is a convenient way to automatically generate mappings based on the fields present in the indexed documents, but it may not always result in the desired mapping behavior.
Overall, field mappings are an important aspect of indexing and searching in Elasticsearch, and they can be customized to achieve more specific indexing and search behavior. By defining the correct mapping for each field, users can ensure accurate and efficient indexing and searching of their data.