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feat: EXPOSED-238 Support EXPLAIN statements (#2022)
Add ExplainQuery class that processes EXPLAIN statements for all valid wrapped statements. The constructor uses 2 new Transaction properties to ensure that the wrapped statements are not executed and that the internal statements is passed to the invoking instance. Add an ExplainResultRow class so that the explain query can be executed and iterated over in a similar manner to a standard query. This class currently is only good for printing a readable string version of the results and needs getters. Add unit tests.
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exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/ExplainQuery.kt
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| @@ -0,0 +1,118 @@ | ||
| package org.jetbrains.exposed.sql | ||
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| import org.jetbrains.exposed.sql.statements.Statement | ||
| import org.jetbrains.exposed.sql.statements.StatementType | ||
| import org.jetbrains.exposed.sql.statements.api.PreparedStatementApi | ||
| import org.jetbrains.exposed.sql.transactions.TransactionManager | ||
| import java.sql.ResultSet | ||
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| /** | ||
| * Represents the SQL query that obtains information about a statement execution plan. | ||
| * | ||
| * @param analyze Whether the statement whose execution plan is being queried should actually be executed as well. | ||
| * @param options String of comma-separated parameters to append after the `EXPLAIN` keyword. | ||
| */ | ||
| open class ExplainQuery( | ||
| val analyze: Boolean, | ||
| val options: String?, | ||
| private val internalStatement: Statement<*> | ||
| ) : Iterable<ExplainResultRow>, Statement<ResultSet>(StatementType.SHOW, emptyList()) { | ||
| private val transaction | ||
| get() = TransactionManager.current() | ||
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| override fun PreparedStatementApi.executeInternal(transaction: Transaction): ResultSet = executeQuery() | ||
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| override fun arguments(): Iterable<Iterable<Pair<IColumnType, Any?>>> = internalStatement.arguments() | ||
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| override fun prepareSQL(transaction: Transaction, prepared: Boolean): String { | ||
| val internalSql = internalStatement.prepareSQL(transaction, prepared) | ||
| return transaction.db.dialect.functionProvider.explain(analyze, options, internalSql, transaction) | ||
| } | ||
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| override fun iterator(): Iterator<ExplainResultRow> { | ||
| val resultIterator = ResultIterator(transaction.exec(this)!!) | ||
| return Iterable { resultIterator }.iterator() | ||
| } | ||
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| private inner class ResultIterator(private val rs: ResultSet) : Iterator<ExplainResultRow> { | ||
| private val fieldIndex: Map<String, Int> = List(rs.metaData.columnCount) { i -> | ||
| rs.metaData.getColumnName(i + 1) to i | ||
| }.toMap() | ||
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| private var hasNext = false | ||
| set(value) { | ||
| field = value | ||
| if (!field) { | ||
| rs.statement?.close() | ||
| transaction.openResultSetsCount-- | ||
| } | ||
| } | ||
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| init { | ||
| hasNext = rs.next() | ||
| } | ||
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| override fun hasNext(): Boolean = hasNext | ||
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| override operator fun next(): ExplainResultRow { | ||
| if (!hasNext) throw NoSuchElementException() | ||
| val result = ExplainResultRow.create(rs, fieldIndex) | ||
| hasNext = rs.next() | ||
| return result | ||
| } | ||
| } | ||
| } | ||
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| /** | ||
| * A row of data representing a single record retrieved from a database result set about a statement execution plan. | ||
| * | ||
| * @param fieldIndex Mapping of the field names stored on this row to their index positions. | ||
| */ | ||
| class ExplainResultRow( | ||
| val fieldIndex: Map<String, Int>, | ||
| private val data: Array<Any?> | ||
| ) { | ||
| override fun toString(): String = fieldIndex.entries.joinToString { "${it.key}=${data[it.value]}" } | ||
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| companion object { | ||
| /** Creates an [ExplainResultRow] storing all fields in [fieldIndex] with their values retrieved from a [ResultSet]. */ | ||
| fun create(rs: ResultSet, fieldIndex: Map<String, Int>): ExplainResultRow { | ||
| val fieldValues = arrayOfNulls<Any?>(fieldIndex.size) | ||
| fieldIndex.values.forEach { index -> | ||
| fieldValues[index] = rs.getObject(index + 1) | ||
| } | ||
| return ExplainResultRow(fieldIndex, fieldValues) | ||
| } | ||
| } | ||
| } | ||
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| /** | ||
| * Creates an [ExplainQuery] using the `EXPLAIN` keyword, which obtains information about a statement execution plan. | ||
| * | ||
| * **Note:** This operation is not supported by all vendors, please check the documentation. | ||
| * | ||
| * @param analyze (optional) Whether the statement whose execution plan is being queried should actually be executed as well. | ||
| * **Note:** The `ANALYZE` parameter is not supported by all vendors, please check the documentation. | ||
| * @param options (optional) String of comma-separated parameters to append after the `EXPLAIN` keyword. | ||
| * **Note:** Optional parameters are not supported by all vendors, please check the documentation. | ||
| * @param body The statement for which an execution plan should be queried. This can be a `SELECT`, `INSERT`, | ||
| * `REPLACE`, `UPDATE` or `DELETE` statement. | ||
| * @sample org.jetbrains.exposed.sql.tests.shared.dml.ExplainTests.testExplainWithStatementsNotExecuted | ||
| */ | ||
| fun Transaction.explain( | ||
| analyze: Boolean = false, | ||
| options: String? = null, | ||
| body: Transaction.() -> Any? | ||
| ): ExplainQuery { | ||
| val query = try { | ||
| blockStatementExecution = true | ||
| val internalStatement = body() as? Statement<*> ?: explainStatement | ||
| checkNotNull(internalStatement) { "A valid query or statement must be provided to the EXPLAIN body." } | ||
| ExplainQuery(analyze, options, internalStatement) | ||
| } finally { | ||
| explainStatement = null | ||
| blockStatementExecution = false | ||
| } | ||
|
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| return query | ||
| } |
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