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JdbcRelationProvider

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

Note

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(
  sqlContext: SQLContext,
  parameters: Map[String, String]): BaseRelation

createRelation is part of the RelationProvider abstraction.

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

NOTE: createRelation uses partitionColumn, lowerBound, upperBound and numPartitions.

In the end, createRelation creates a datasources/jdbc/JDBCRelation.md#creating-instance[JDBCRelation] with datasources/jdbc/JDBCRelation.md#columnPartition[column partitions] (and JDBCOptions).

Writing Rows of Structured Query (DataFrame) to Table Using JDBC

createRelation(
  sqlContext: SQLContext,
  mode: SaveMode,
  parameters: Map[String, String],
  df: DataFrame): BaseRelation

createRelation is part of the CreatableRelationProvider abstraction.

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

createRelation...FIXME

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

NOTE: 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).

[[createRelation-CreatableRelationProvider-SaveMode]] .createRelation and SaveMode [cols="1,2",options="header",width="100%"] |=== | Name | Description

| Append | Saves the records to the table.

| ErrorIfExists a| Throws a AnalysisException with the message:

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

| Ignore | Does nothing.

| Overwrite a| Truncates or drops the table

NOTE: createRelation truncates the table only when truncate JDBC option is enabled and JdbcDialect.md#isCascadingTruncateTable[isCascadingTruncateTable] is disabled. |===

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

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