RelationProvider — Relations with Pre-Defined Schema¶
RelationProvider is an abstraction of providers for relational data sources with schema inference (schema discovery). In other words, the schema of a relation is pre-defined (fixed), and a user-specified schema is not allowed.
Use SchemaRelationProvider for data source providers that require a user-defined schema.
createRelation( sqlContext: SQLContext, parameters: Map[String, String]): BaseRelation
DataSourceis requested to resolve a relation
It is a common pattern while developing a custom data source to use RelationProvider.createRelation with CreatableRelationProvider when requested for a relation (after writing out a structured query).