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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.spark.sql.jdbc
import java.sql.{Connection, Date, Driver, Statement, Timestamp}
import java.time.{Instant, LocalDate, LocalDateTime}
import java.util
import scala.collection.mutable.ArrayBuilder
import scala.util.control.NonFatal
import org.apache.commons.lang3.StringUtils
import org.apache.spark.annotation.{DeveloperApi, Since}
import org.apache.spark.internal.Logging
import org.apache.spark.sql.AnalysisException
import org.apache.spark.sql.catalyst.CatalystTypeConverters
import org.apache.spark.sql.catalyst.util.{DateFormatter, DateTimeUtils, TimestampFormatter}
import org.apache.spark.sql.catalyst.util.DateTimeUtils.{localDateTimeToMicros, toJavaTimestampNoRebase}
import org.apache.spark.sql.connector.catalog.{Identifier, TableChange}
import org.apache.spark.sql.connector.catalog.TableChange._
import org.apache.spark.sql.connector.catalog.functions.UnboundFunction
import org.apache.spark.sql.connector.catalog.index.TableIndex
import org.apache.spark.sql.connector.expressions.{Expression, Literal, NamedReference}
import org.apache.spark.sql.connector.expressions.aggregate.AggregateFunc
import org.apache.spark.sql.connector.util.V2ExpressionSQLBuilder
import org.apache.spark.sql.errors.QueryCompilationErrors
import org.apache.spark.sql.execution.datasources.jdbc.{DriverRegistry, JDBCOptions, JdbcOptionsInWrite, JdbcUtils}
import org.apache.spark.sql.execution.datasources.jdbc.connection.ConnectionProvider
import org.apache.spark.sql.execution.datasources.v2.TableSampleInfo
import org.apache.spark.sql.internal.SQLConf
import org.apache.spark.sql.types._
/**
* :: DeveloperApi ::
* A database type definition coupled with the jdbc type needed to send null
* values to the database.
* @param databaseTypeDefinition The database type definition
* @param jdbcNullType The jdbc type (as defined in java.sql.Types) used to
* send a null value to the database.
*/
@DeveloperApi
case class JdbcType(databaseTypeDefinition : String, jdbcNullType : Int)
/**
* :: DeveloperApi ::
* Encapsulates everything (extensions, workarounds, quirks) to handle the
* SQL dialect of a certain database or jdbc driver.
* Lots of databases define types that aren't explicitly supported
* by the JDBC spec. Some JDBC drivers also report inaccurate
* information---for instance, BIT(n{@literal >}1) being reported as a BIT type is quite
* common, even though BIT in JDBC is meant for single-bit values. Also, there
* does not appear to be a standard name for an unbounded string or binary
* type; we use BLOB and CLOB by default but override with database-specific
* alternatives when these are absent or do not behave correctly.
*
* Currently, the only thing done by the dialect is type mapping.
* `getCatalystType` is used when reading from a JDBC table and `getJDBCType`
* is used when writing to a JDBC table. If `getCatalystType` returns `null`,
* the default type handling is used for the given JDBC type. Similarly,
* if `getJDBCType` returns `(null, None)`, the default type handling is used
* for the given Catalyst type.
*/
@DeveloperApi
abstract class JdbcDialect extends Serializable with Logging {
/**
* Check if this dialect instance can handle a certain jdbc url.
* @param url the jdbc url.
* @return True if the dialect can be applied on the given jdbc url.
* @throws NullPointerException if the url is null.
*/
def canHandle(url : String): Boolean
/**
* Get the custom datatype mapping for the given jdbc meta information.
* @param sqlType The sql type (see java.sql.Types)
* @param typeName The sql type name (e.g. "BIGINT UNSIGNED")
* @param size The size of the type.
* @param md Result metadata associated with this type.
* @return The actual DataType (subclasses of [[org.apache.spark.sql.types.DataType]])
* or null if the default type mapping should be used.
*/
def getCatalystType(
sqlType: Int, typeName: String, size: Int, md: MetadataBuilder): Option[DataType] = None
/**
* Retrieve the jdbc / sql type for a given datatype.
* @param dt The datatype (e.g. [[org.apache.spark.sql.types.StringType]])
* @return The new JdbcType if there is an override for this DataType
*/
def getJDBCType(dt: DataType): Option[JdbcType] = None
/**
* Converts an instance of `java.sql.Timestamp` to a custom `java.sql.Timestamp` value.
* @param t represents a specific instant in time based on
* the hybrid calendar which combines Julian and
* Gregorian calendars.
* @return the timestamp value to convert to
* @throws IllegalArgumentException if t is null
*/
@Since("3.5.0")
def convertJavaTimestampToTimestamp(t: Timestamp): Timestamp = t
/**
* Convert java.sql.Timestamp to a LocalDateTime representing the same wall-clock time as the
* value stored in a remote database.
* JDBC dialects should override this function to provide implementations that suit their
* JDBC drivers.
* @param t Timestamp returned from JDBC driver getTimestamp method.
* @return A LocalDateTime representing the same wall clock time as the timestamp in database.
*/
@Since("3.5.0")
def convertJavaTimestampToTimestampNTZ(t: Timestamp): LocalDateTime = {
DateTimeUtils.microsToLocalDateTime(DateTimeUtils.fromJavaTimestampNoRebase(t))
}
/**
* Converts a LocalDateTime representing a TimestampNTZ type to an
* instance of `java.sql.Timestamp`.
* @param ldt representing a TimestampNTZType.
* @return A Java Timestamp representing this LocalDateTime.
*/
@Since("3.5.0")
def convertTimestampNTZToJavaTimestamp(ldt: LocalDateTime): Timestamp = {
val micros = localDateTimeToMicros(ldt)
toJavaTimestampNoRebase(micros)
}
/**
* Returns a factory for creating connections to the given JDBC URL.
* In general, creating a connection has nothing to do with JDBC partition id.
* But sometimes it is needed, such as a database with multiple shard nodes.
* @param options - JDBC options that contains url, table and other information.
* @return The factory method for creating JDBC connections with the RDD partition ID. -1 means
the connection is being created at the driver side.
* @throws IllegalArgumentException if the driver could not open a JDBC connection.
*/
@Since("3.3.0")
def createConnectionFactory(options: JDBCOptions): Int => Connection = {
val driverClass: String = options.driverClass
(partitionId: Int) => {
DriverRegistry.register(driverClass)
val driver: Driver = DriverRegistry.get(driverClass)
val connection =
ConnectionProvider.create(driver, options.parameters, options.connectionProviderName)
require(connection != null,
s"The driver could not open a JDBC connection. Check the URL: ${options.url}")
connection
}
}
/**
* Quotes the identifier. This is used to put quotes around the identifier in case the column
* name is a reserved keyword, or in case it contains characters that require quotes (e.g. space).
*/
def quoteIdentifier(colName: String): String = {
s""""$colName""""
}
/**
* Create the table if the table does not exist.
* To allow certain options to append when create a new table, which can be
* table_options or partition_options.
* E.g., "CREATE TABLE t (name string) ENGINE=InnoDB DEFAULT CHARSET=utf8"
* @param statement
* @param tableName
* @param strSchema
* @param options
*/
def createTable(
statement: Statement,
tableName: String,
strSchema: String,
options: JdbcOptionsInWrite): Unit = {
val createTableOptions = options.createTableOptions
statement.executeUpdate(s"CREATE TABLE $tableName ($strSchema) $createTableOptions")
}
/**
* Get the SQL query that should be used to find if the given table exists. Dialects can
* override this method to return a query that works best in a particular database.
* @param table The name of the table.
* @return The SQL query to use for checking the table.
*/
def getTableExistsQuery(table: String): String = {
s"SELECT * FROM $table WHERE 1=0"
}
/**
* The SQL query that should be used to discover the schema of a table. It only needs to
* ensure that the result set has the same schema as the table, such as by calling
* "SELECT * ...". Dialects can override this method to return a query that works best in a
* particular database.
* @param table The name of the table.
* @return The SQL query to use for discovering the schema.
*/
@Since("2.1.0")
def getSchemaQuery(table: String): String = {
s"SELECT * FROM $table WHERE 1=0"
}
/**
* The SQL query that should be used to truncate a table. Dialects can override this method to
* return a query that is suitable for a particular database. For PostgreSQL, for instance,
* a different query is used to prevent "TRUNCATE" affecting other tables.
* @param table The table to truncate
* @return The SQL query to use for truncating a table
*/
@Since("2.3.0")
def getTruncateQuery(table: String): String = {
getTruncateQuery(table, isCascadingTruncateTable)
}
/**
* The SQL query that should be used to truncate a table. Dialects can override this method to
* return a query that is suitable for a particular database. For PostgreSQL, for instance,
* a different query is used to prevent "TRUNCATE" affecting other tables.
* @param table The table to truncate
* @param cascade Whether or not to cascade the truncation
* @return The SQL query to use for truncating a table
*/
@Since("2.4.0")
def getTruncateQuery(
table: String,
cascade: Option[Boolean] = isCascadingTruncateTable): String = {
s"TRUNCATE TABLE $table"
}
/**
* Override connection specific properties to run before a select is made. This is in place to
* allow dialects that need special treatment to optimize behavior.
* @param connection The connection object
* @param properties The connection properties. This is passed through from the relation.
*/
def beforeFetch(connection: Connection, properties: Map[String, String]): Unit = {
}
/**
* Escape special characters in SQL string literals.
* @param value The string to be escaped.
* @return Escaped string.
*/
@Since("2.3.0")
protected[jdbc] def escapeSql(value: String): String =
if (value == null) null else StringUtils.replace(value, "'", "''")
/**
* Converts value to SQL expression.
* @param value The value to be converted.
* @return Converted value.
*/
@Since("2.3.0")
def compileValue(value: Any): Any = value match {
case stringValue: String => s"'${escapeSql(stringValue)}'"
case timestampValue: Timestamp => "'" + timestampValue + "'"
case timestampValue: Instant =>
val timestampFormatter = TimestampFormatter.getFractionFormatter(
DateTimeUtils.getZoneId(SQLConf.get.sessionLocalTimeZone))
s"'${timestampFormatter.format(timestampValue)}'"
case dateValue: Date => "'" + dateValue + "'"
case dateValue: LocalDate => s"'${DateFormatter().format(dateValue)}'"
case arrayValue: Array[Any] => arrayValue.map(compileValue).mkString(", ")
case _ => value
}
private[jdbc] class JDBCSQLBuilder extends V2ExpressionSQLBuilder {
override def visitLiteral(literal: Literal[_]): String = {
Option(literal.value()).map(v =>
compileValue(CatalystTypeConverters.convertToScala(v, literal.dataType())).toString)
.getOrElse(super.visitLiteral(literal))
}
override def visitNamedReference(namedRef: NamedReference): String = {
if (namedRef.fieldNames().length > 1) {
throw QueryCompilationErrors.commandNotSupportNestedColumnError(
"Filter push down", namedRef.toString)
}
quoteIdentifier(namedRef.fieldNames.head)
}
override def visitCast(l: String, dataType: DataType): String = {
val databaseTypeDefinition =
getJDBCType(dataType).map(_.databaseTypeDefinition).getOrElse(dataType.typeName)
s"CAST($l AS $databaseTypeDefinition)"
}
override def visitSQLFunction(funcName: String, inputs: Array[String]): String = {
if (isSupportedFunction(funcName)) {
s"""${dialectFunctionName(funcName)}(${inputs.mkString(", ")})"""
} else {
// The framework will catch the error and give up the push-down.
// Please see `JdbcDialect.compileExpression(expr: Expression)` for more details.
throw new UnsupportedOperationException(
s"${this.getClass.getSimpleName} does not support function: $funcName")
}
}
override def visitAggregateFunction(
funcName: String, isDistinct: Boolean, inputs: Array[String]): String = {
if (isSupportedFunction(funcName)) {
super.visitAggregateFunction(dialectFunctionName(funcName), isDistinct, inputs)
} else {
throw new UnsupportedOperationException(
s"${this.getClass.getSimpleName} does not support aggregate function: $funcName");
}
}
protected def dialectFunctionName(funcName: String): String = funcName
override def visitOverlay(inputs: Array[String]): String = {
if (isSupportedFunction("OVERLAY")) {
super.visitOverlay(inputs)
} else {
throw new UnsupportedOperationException(
s"${this.getClass.getSimpleName} does not support function: OVERLAY")
}
}
override def visitTrim(direction: String, inputs: Array[String]): String = {
if (isSupportedFunction("TRIM")) {
super.visitTrim(direction, inputs)
} else {
throw new UnsupportedOperationException(
s"${this.getClass.getSimpleName} does not support function: TRIM")
}
}
}
/**
* Returns whether the database supports function.
* @param funcName Upper-cased function name
* @return True if the database supports function.
*/
@Since("3.3.0")
def isSupportedFunction(funcName: String): Boolean = false
/**
* Converts V2 expression to String representing a SQL expression.
* @param expr The V2 expression to be converted.
* @return Converted value.
*/
@Since("3.3.0")
def compileExpression(expr: Expression): Option[String] = {
val jdbcSQLBuilder = new JDBCSQLBuilder()
try {
Some(jdbcSQLBuilder.build(expr))
} catch {
case NonFatal(e) =>
logWarning("Error occurs while compiling V2 expression", e)
None
}
}
/**
* Converts aggregate function to String representing a SQL expression.
* @param aggFunction The aggregate function to be converted.
* @return Converted value.
*/
@Since("3.3.0")
@deprecated("use org.apache.spark.sql.jdbc.JdbcDialect.compileExpression instead.", "3.4.0")
def compileAggregate(aggFunction: AggregateFunc): Option[String] = compileExpression(aggFunction)
/**
* List the user-defined functions in jdbc dialect.
* @return a sequence of tuple from function name to user-defined function.
*/
def functions: Seq[(String, UnboundFunction)] = Nil
/**
* Create schema with an optional comment. Empty string means no comment.
*/
def createSchema(statement: Statement, schema: String, comment: String): Unit = {
val schemaCommentQuery = if (comment.nonEmpty) {
// We generate comment query here so that it can fail earlier without creating the schema.
getSchemaCommentQuery(schema, comment)
} else {
comment
}
statement.executeUpdate(s"CREATE SCHEMA ${quoteIdentifier(schema)}")
if (comment.nonEmpty) {
statement.executeUpdate(schemaCommentQuery)
}
}
/**
* Check schema exists or not.
*/
def schemasExists(conn: Connection, options: JDBCOptions, schema: String): Boolean = {
val rs = conn.getMetaData.getSchemas(null, schema)
while (rs.next()) {
if (rs.getString(1) == schema) return true;
}
false
}
/**
* Lists all the schemas in this table.
*/
def listSchemas(conn: Connection, options: JDBCOptions): Array[Array[String]] = {
val schemaBuilder = ArrayBuilder.make[Array[String]]
val rs = conn.getMetaData.getSchemas()
while (rs.next()) {
schemaBuilder += Array(rs.getString(1))
}
schemaBuilder.result
}
/**
* Return Some[true] iff `TRUNCATE TABLE` causes cascading default.
* Some[true] : TRUNCATE TABLE causes cascading.
* Some[false] : TRUNCATE TABLE does not cause cascading.
* None: The behavior of TRUNCATE TABLE is unknown (default).
*/
def isCascadingTruncateTable(): Option[Boolean] = None
/**
* Rename an existing table.
*
* @param oldTable The existing table.
* @param newTable New name of the table.
* @return The SQL statement to use for renaming the table.
*/
@deprecated("Please override renameTable method with identifiers", "3.5.0")
def renameTable(oldTable: String, newTable: String): String = {
s"ALTER TABLE $oldTable RENAME TO $newTable"
}
/**
* Rename an existing table.
*
* @param oldTable The existing table.
* @param newTable New name of the table.
* @return The SQL statement to use for renaming the table.
*/
@Since("3.5.0")
def renameTable(oldTable: Identifier, newTable: Identifier): String = {
s"ALTER TABLE ${getFullyQualifiedQuotedTableName(oldTable)} RENAME TO " +
s"${getFullyQualifiedQuotedTableName(newTable)}"
}
/**
* Alter an existing table.
*
* @param tableName The name of the table to be altered.
* @param changes Changes to apply to the table.
* @return The SQL statements to use for altering the table.
*/
def alterTable(
tableName: String,
changes: Seq[TableChange],
dbMajorVersion: Int): Array[String] = {
val updateClause = ArrayBuilder.make[String]
for (change <- changes) {
change match {
case add: AddColumn if add.fieldNames.length == 1 =>
val dataType = JdbcUtils.getJdbcType(add.dataType(), this).databaseTypeDefinition
val name = add.fieldNames
updateClause += getAddColumnQuery(tableName, name(0), dataType)
case rename: RenameColumn if rename.fieldNames.length == 1 =>
val name = rename.fieldNames
updateClause += getRenameColumnQuery(tableName, name(0), rename.newName, dbMajorVersion)
case delete: DeleteColumn if delete.fieldNames.length == 1 =>
val name = delete.fieldNames
updateClause += getDeleteColumnQuery(tableName, name(0))
case updateColumnType: UpdateColumnType if updateColumnType.fieldNames.length == 1 =>
val name = updateColumnType.fieldNames
val dataType = JdbcUtils.getJdbcType(updateColumnType.newDataType(), this)
.databaseTypeDefinition
updateClause += getUpdateColumnTypeQuery(tableName, name(0), dataType)
case updateNull: UpdateColumnNullability if updateNull.fieldNames.length == 1 =>
val name = updateNull.fieldNames
updateClause += getUpdateColumnNullabilityQuery(tableName, name(0), updateNull.nullable())
case _ =>
throw QueryCompilationErrors.unsupportedTableChangeInJDBCCatalogError(change)
}
}
updateClause.result()
}
def getAddColumnQuery(tableName: String, columnName: String, dataType: String): String =
s"ALTER TABLE $tableName ADD COLUMN ${quoteIdentifier(columnName)} $dataType"
def getRenameColumnQuery(
tableName: String,
columnName: String,
newName: String,
dbMajorVersion: Int): String =
s"ALTER TABLE $tableName RENAME COLUMN ${quoteIdentifier(columnName)} TO" +
s" ${quoteIdentifier(newName)}"
def getDeleteColumnQuery(tableName: String, columnName: String): String =
s"ALTER TABLE $tableName DROP COLUMN ${quoteIdentifier(columnName)}"
def getUpdateColumnTypeQuery(
tableName: String,
columnName: String,
newDataType: String): String =
s"ALTER TABLE $tableName ALTER COLUMN ${quoteIdentifier(columnName)} $newDataType"
def getUpdateColumnNullabilityQuery(
tableName: String,
columnName: String,
isNullable: Boolean): String = {
val nullable = if (isNullable) "NULL" else "NOT NULL"
s"ALTER TABLE $tableName ALTER COLUMN ${quoteIdentifier(columnName)} SET $nullable"
}
def getTableCommentQuery(table: String, comment: String): String = {
s"COMMENT ON TABLE $table IS '$comment'"
}
def getSchemaCommentQuery(schema: String, comment: String): String = {
s"COMMENT ON SCHEMA ${quoteIdentifier(schema)} IS '$comment'"
}
def removeSchemaCommentQuery(schema: String): String = {
s"COMMENT ON SCHEMA ${quoteIdentifier(schema)} IS NULL"
}
def dropSchema(schema: String, cascade: Boolean): String = {
if (cascade) {
s"DROP SCHEMA ${quoteIdentifier(schema)} CASCADE"
} else {
s"DROP SCHEMA ${quoteIdentifier(schema)}"
}
}
/**
* Build a create index SQL statement.
*
* @param indexName the name of the index to be created
* @param tableIdent the table on which index to be created
* @param columns the columns on which index to be created
* @param columnsProperties the properties of the columns on which index to be created
* @param properties the properties of the index to be created
* @return the SQL statement to use for creating the index.
*/
def createIndex(
indexName: String,
tableIdent: Identifier,
columns: Array[NamedReference],
columnsProperties: util.Map[NamedReference, util.Map[String, String]],
properties: util.Map[String, String]): String = {
throw new UnsupportedOperationException("createIndex is not supported")
}
/**
* Checks whether an index exists
*
* @param indexName the name of the index
* @param tableIdent the table on which index to be checked
* @param options JDBCOptions of the table
* @return true if the index with `indexName` exists in the table with `tableName`,
* false otherwise
*/
def indexExists(
conn: Connection,
indexName: String,
tableIdent: Identifier,
options: JDBCOptions): Boolean = {
throw new UnsupportedOperationException("indexExists is not supported")
}
/**
* Build a drop index SQL statement.
*
* @param indexName the name of the index to be dropped.
* @param tableIdent the table on which index to be dropped.
* @return the SQL statement to use for dropping the index.
*/
def dropIndex(indexName: String, tableIdent: Identifier): String = {
throw new UnsupportedOperationException("dropIndex is not supported")
}
/**
* Lists all the indexes in this table.
*/
def listIndexes(
conn: Connection,
tableIdent: Identifier,
options: JDBCOptions): Array[TableIndex] = {
throw new UnsupportedOperationException("listIndexes is not supported")
}
/**
* Gets a dialect exception, classifies it and wraps it by `AnalysisException`.
* @param message The error message to be placed to the returned exception.
* @param e The dialect specific exception.
* @return `AnalysisException` or its sub-class.
*/
def classifyException(message: String, e: Throwable): AnalysisException = {
new AnalysisException(message, cause = Some(e))
}
/**
* Returns the LIMIT clause for the SELECT statement
*/
def getLimitClause(limit: Integer): String = {
if (limit > 0) s"LIMIT $limit" else ""
}
/**
* Returns the OFFSET clause for the SELECT statement
*/
def getOffsetClause(offset: Integer): String = {
if (offset > 0) s"OFFSET $offset" else ""
}
/**
* Returns the SQL builder for the SELECT statement.
*/
def getJdbcSQLQueryBuilder(options: JDBCOptions): JdbcSQLQueryBuilder =
new JdbcSQLQueryBuilder(this, options)
/**
* Returns ture if dialect supports LIMIT clause.
*
* Note: Some build-in dialect supports LIMIT clause with some trick, please see:
* {@link OracleDialect.OracleSQLQueryBuilder} and
* {@link MsSqlServerDialect.MsSqlServerSQLQueryBuilder}.
*/
def supportsLimit: Boolean = false
/**
* Returns ture if dialect supports OFFSET clause.
*
* Note: Some build-in dialect supports OFFSET clause with some trick, please see:
* {@link OracleDialect.OracleSQLQueryBuilder} and
* {@link MySQLDialect.MySQLSQLQueryBuilder}.
*/
def supportsOffset: Boolean = false
def supportsTableSample: Boolean = false
def getTableSample(sample: TableSampleInfo): String =
throw new UnsupportedOperationException("TableSample is not supported by this data source")
/**
* Return the DB-specific quoted and fully qualified table name
*/
@Since("3.5.0")
def getFullyQualifiedQuotedTableName(ident: Identifier): String = {
(ident.namespace() :+ ident.name()).map(quoteIdentifier).mkString(".")
}
}
/**
* :: DeveloperApi ::
* Registry of dialects that apply to every new jdbc `org.apache.spark.sql.DataFrame`.
*
* If multiple matching dialects are registered then all matching ones will be
* tried in reverse order. A user-added dialect will thus be applied first,
* overwriting the defaults.
*
* @note All new dialects are applied to new jdbc DataFrames only. Make
* sure to register your dialects first.
*/
@DeveloperApi
object JdbcDialects {
/**
* Register a dialect for use on all new matching jdbc `org.apache.spark.sql.DataFrame`.
* Reading an existing dialect will cause a move-to-front.
*
* @param dialect The new dialect.
*/
def registerDialect(dialect: JdbcDialect) : Unit = {
dialects = dialect :: dialects.filterNot(_ == dialect)
}
/**
* Unregister a dialect. Does nothing if the dialect is not registered.
*
* @param dialect The jdbc dialect.
*/
def unregisterDialect(dialect : JdbcDialect) : Unit = {
dialects = dialects.filterNot(_ == dialect)
}
private[this] var dialects = List[JdbcDialect]()
registerDialect(MySQLDialect)
registerDialect(PostgresDialect)
registerDialect(DB2Dialect)
registerDialect(MsSqlServerDialect)
registerDialect(DerbyDialect)
registerDialect(OracleDialect)
registerDialect(TeradataDialect)
registerDialect(H2Dialect)
/**
* Fetch the JdbcDialect class corresponding to a given database url.
*/
def get(url: String): JdbcDialect = {
val matchingDialects = dialects.filter(_.canHandle(url))
matchingDialects.length match {
case 0 => NoopDialect
case 1 => matchingDialects.head
case _ => new AggregatedDialect(matchingDialects)
}
}
}
/**
* NOOP dialect object, always returning the neutral element.
*/
private[spark] object NoopDialect extends JdbcDialect {
override def canHandle(url : String): Boolean = true
}
