JdbcRelationProvider is a DataSourceRegister and registers itself to handle jdbc data source format.

JdbcRelationProvider uses META-INF/services/org.apache.spark.sql.sources.DataSourceRegister file for the registration which is available in the source code of Apache Spark.

JdbcRelationProvider is a RelationProvider and a CreatableRelationProvider.

JdbcRelationProvider is used when DataFrameReader is requested to load data from jdbc data source.

val table = spark.read.jdbc(...)

// or in a more verbose way
val table = spark.read.format("jdbc").load(...)

Loading Data from Table Using JDBC — createRelation Method (from RelationProvider)

  sqlContext: SQLContext,
  parameters: Map[String, String]): BaseRelation
createRelation is part of RelationProvider Contract to create a BaseRelation for reading.

createRelation creates a JDBCPartitioningInfo (using JDBCOptions and the input parameters that correspond to the Options for JDBC Data Source).

createRelation uses partitionColumn, lowerBound, upperBound and numPartitions.

In the end, createRelation creates a JDBCRelation with column partitions (and JDBCOptions).

Writing Rows of Structured Query (DataFrame) to Table Using JDBC — createRelation Method (from CreatableRelationProvider)

  sqlContext: SQLContext,
  mode: SaveMode,
  parameters: Map[String, String],
  df: DataFrame): BaseRelation
createRelation is part of the CreatableRelationProvider Contract to write the rows of a structured query (a DataFrame) to an external data source.

Internally, createRelation creates a JDBCOptions (from the input parameters).

createRelation reads caseSensitiveAnalysis (using the input sqlContext).

createRelation checks whether the table (given dbtable and url options in the input parameters) exists.

createRelation uses a database-specific JdbcDialect to check whether a table exists.

createRelation branches off per whether the table already exists in the database or not.

If the table does not exist, createRelation creates the table (by executing CREATE TABLE with createTableColumnTypes and createTableOptions options from the input parameters) and writes the rows to the database in a single transaction.

If however the table does exist, createRelation branches off per SaveMode (see the following createRelation and SaveMode).

Table 1. createRelation and SaveMode
Name Description


Saves the records to the table.


Throws a AnalysisException with the message:

Table or view '[table]' already exists. SaveMode: ErrorIfExists.


Does nothing.


Truncates or drops the table

createRelation truncates the table only when truncate JDBC option is enabled and isCascadingTruncateTable is disabled.

In the end, createRelation closes the JDBC connection to the database and creates a JDBCRelation.

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