add-isolation-levels (#28)

* add-isolation-levels * document-it * remove-overloading * fix-README * revert-to-overloading --------- Co-authored-by: AlexKuznetsov <[email protected]> Co-authored-by: chad-moller-target <[email protected]>
target · Oct 10, 2023 · e7ad85a · e7ad85a
1 parent e130972
commit e7ad85a
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diff --git a/README.md b/README.md
@@ -589,7 +589,7 @@ At the end of the withAutoCommit block, the AutoCommit ConnectionSession will be
 ## withTransaction
 
 By using a Transaction ConnectionSession, changes will NOT be immediately committed to the database. Which allows for
-multiple features listed below. If any of these features are required, use withTransaction.
+multiple features listed below. If any of these features are required, use withTransaction. Also use withTransaction if you need to specify isolation level.
 
 * Commit - Commits any existing changes to the database and clears any Savepoints and Locks
 * Rollback - Reverts the changes since the most recent commit, or the beginning of the ConnectionSession if no commits
@@ -603,6 +603,18 @@ At the end of the withTransaction block, if the block is exited normally the Tra
 exception is thrown, the Transaction will be rolled back. After the final commit/rollback, the Transaction ConnectionSession
 will be closed.
 
+### withTransaction - How to Specify Isolation levels
+
+By default, all transactions run with `TRANSACTION_READ_COMMITTED`isolation level. The following shows how to specify a higher one:
+
+```kotlin
+  db.withTransaction(isolationLevel = Db.IsolationLevel.TRANSACTION_REPEATABLE_READ) 
+
+  db.withTransaction(isolationLevel = Db.IsolationLevel.TRANSACTION_SERIALIZABLE) 
+```
+
+When the transaction is over, isolation level is restored to the default, TRANSACTION_READ_COMMITTED.
+
 ## DataSource configuration & AutoCommit
 
 A dataSource has a default setting for the autocommit flag which can be configured. But the individual connections can

diff --git a/src/main/kotlin/com/target/liteforjdbc/Db.kt b/src/main/kotlin/com/target/liteforjdbc/Db.kt
@@ -118,20 +118,34 @@ open class Db(
      * or rolls back if it throws an exception. This is required to perform any DB interactions that need transaction
      * support.
      */
-    fun <T> withTransaction(block: (Transaction) -> T): T {
+    fun <T> withTransaction(
+        isolationLevel: IsolationLevel,
+        block: (Transaction) -> T
+    ): T {
         val transaction = Transaction(connection = dataSource.connection)
-        transaction.use {
+        val currentIsolationLevel = transaction.connection.transactionIsolation
+        return transaction.use {
             try {
+                transaction.connection.transactionIsolation = isolationLevel.intCode
                 val result = block(transaction)
                 transaction.commit()
-                return result
+                result
             } catch (t: Throwable) {
                 transaction.rollback()
                 throw t
+            } finally {
+                transaction.connection.transactionIsolation = currentIsolationLevel
             }
         }
     }
 
+    /**
+     * Uses a com.target.liteforjdbc.Transaction, and commits it once to the block is executed successfully,
+     * or rolls back if it throws an exception. This is required to perform any DB interactions that need transaction
+     * support.
+     */
+    fun <T> withTransaction(block: (Transaction) -> T): T = withTransaction(IsolationLevel.TRANSACTION_READ_COMMITTED, block)
+
     /**
      * Uses a com.target.liteforjdbc.AutoCommit and closes it once teh block is executed. This can be useful to use a
      * single connection from the DataSource for a series of actions. Using other convenience query methods on this
@@ -169,5 +183,11 @@ open class Db(
      */
     fun isDataSourceHealthy() = useConnection { !it.isClosed }
 
+    enum class IsolationLevel(val intCode: Int) {
+        TRANSACTION_READ_COMMITTED(Connection.TRANSACTION_READ_COMMITTED),
+        TRANSACTION_REPEATABLE_READ(Connection.TRANSACTION_REPEATABLE_READ),
+        TRANSACTION_SERIALIZABLE(Connection.TRANSACTION_SERIALIZABLE)
+    }
+
 }
 
diff --git a/src/test/kotlin/com/target/liteforjdbc/postgres/PostgresSqlIntegrationTest.kt b/src/test/kotlin/com/target/liteforjdbc/postgres/PostgresSqlIntegrationTest.kt
@@ -441,6 +441,34 @@ class PostgresSqlIntegrationTest {
 
         finalCount shouldBe originalCount
     }
+
+    @Test
+    fun setsReadCommittedIsolationLevel() {
+        checkIsolationLevel(Db.IsolationLevel.TRANSACTION_READ_COMMITTED, "read committed")
+    }
+
+    @Test
+    fun setsRepeatableReadIsolationLevel() {
+        checkIsolationLevel(Db.IsolationLevel.TRANSACTION_REPEATABLE_READ, "repeatable read")
+    }
+
+    @Test
+    fun setsSerializatableIsolationLevel() {
+        checkIsolationLevel(Db.IsolationLevel.TRANSACTION_SERIALIZABLE, "serializable")
+    }
+
+    private fun checkIsolationLevel(isolationLevel: Db.IsolationLevel, expected: String) {
+        val level = db.withTransaction(isolationLevel) { transaction ->
+            checkNotNull(
+                transaction.executeQuery(
+                    "SELECT current_setting('transaction_isolation')"
+                ) { resultSet: ResultSet ->
+                    resultSet.getString("current_setting")
+                }
+            )
+        }
+        level shouldBe expected
+    }
 
     private fun tableCount(): Int {
         return checkNotNull(