聊聊flink TableEnvironment的scan操作

序
本文主要研究一下flink TableEnvironment的scan操作
实例
//Scanning a directly registered table
val tab: Table = tableEnv.scan(“tableName”)

//Scanning a table from a registered catalog
val tab: Table = tableEnv.scan(“catalogName”, “dbName”, “tableName”)
scan操作用于从schema读取指定的table，也可以传入catalogName及dbName从指定的catalog及db读取
TableEnvironment.scan
flink-table_2.11-1.7.0-sources.jar!/org/apache/flink/table/api/TableEnvironment.scala
abstract class TableEnvironment(val config: TableConfig) {

private val internalSchema: CalciteSchema = CalciteSchema.createRootSchema(false, false)
private val rootSchema: SchemaPlus = internalSchema.plus()

//……

@throws[TableException]
@varargs
def scan(tablePath: String*): Table = {
scanInternal(tablePath.toArray) match {
case Some(table) => table
case None => throw new TableException(s”Table ‘${tablePath.mkString(“.”)}’ was not found.”)
}
}

private[flink] def scanInternal(tablePath: Array[String]): Option[Table] = {
require(tablePath != null && !tablePath.isEmpty, “tablePath must not be null or empty.”)
val schemaPaths = tablePath.slice(0, tablePath.length – 1)
val schema = getSchema(schemaPaths)
if (schema != null) {
val tableName = tablePath(tablePath.length – 1)
val table = schema.getTable(tableName)
if (table != null) {
return Some(new Table(this, CatalogNode(tablePath, table.getRowType(typeFactory))))
}
}
None
}

private def getSchema(schemaPath: Array[String]): SchemaPlus = {
var schema = rootSchema
for (schemaName <- schemaPath) {
schema = schema.getSubSchema(schemaName)
if (schema == null) {
return schema
}
}
schema
}

//……
}

scan方法内部调用的是scanInternal，scanInternal首先读取catalog及db信息，然后调用getSchema方法来获取schema
getSchema是使用SchemaPlus的getSubSchema来按层次获取SchemaPlus，如果没有指定catalog及db，那么这里返回的是rootSchema
获取到schema之后，就可以从tablePath数组获取tableName(数组最后一个元素)，调用SchemaPlus的getTable方法查找Table

小结

TableEnvironment的scan操作就是从Schema中查找Table，可以使用tableName，或者额外指定catalog及db来查找
getSchema是使用SchemaPlus的getSubSchema来按层次获取SchemaPlus，如果没有指定catalog及db，那么这里返回的是rootSchema
获取到schema之后，就可以从tablePath数组获取tableName(数组最后一个元素)，调用SchemaPlus的getTable方法查找Table

doc
Table API