Sum batch results for inserts (#1641)

* Sum batch results for inserts

When executing a batch insert, the number of inserted rows is the sum of the batch rows instead of the count.

Making this distinction allows extensions of batch insert like
```
class MyBatchInsertStatement(
    table: Table,
) : BatchInsertStatement(table) {
    override fun prepareSQL(transaction: Transaction) = buildString {
        append(super.prepareSQL(transaction))
        append(" ON CONFLICT (id) DO NOTHING")
    }
}
```
where the return value of `execute` is still accurate.

* Add test

exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/statements/InsertStatement.kt

@@ -123,7 +123,7 @@ open class InsertStatement<Key : Any>(val table: Table, val isIgnore: Boolean =
     }
 
     protected open fun PreparedStatementApi.execInsertFunction(): Pair<Int, ResultSet?> {
-        val inserted = if (arguments().count() > 1 || isAlwaysBatch) executeBatch().count() else executeUpdate()
+        val inserted = if (arguments().count() > 1 || isAlwaysBatch) executeBatch().sum() else executeUpdate()
         val rs = if (autoIncColumns.isNotEmpty()) {
             resultSet
         } else null

exposed-tests/src/test/kotlin/org/jetbrains/exposed/sql/tests/shared/dml/InsertTests.kt

@@ -8,6 +8,7 @@ import org.jetbrains.exposed.dao.id.IdTable
 import org.jetbrains.exposed.dao.id.IntIdTable
 import org.jetbrains.exposed.sql.*
 import org.jetbrains.exposed.sql.SqlExpressionBuilder.eq
+import org.jetbrains.exposed.sql.statements.BatchInsertStatement
 import org.jetbrains.exposed.sql.tests.DatabaseTestsBase
 import org.jetbrains.exposed.sql.tests.TestDB
 import org.jetbrains.exposed.sql.tests.currentDialectTest
@@ -574,4 +575,35 @@ class InsertTests : DatabaseTestsBase() {
         }
 
     }
+
+    class BatchInsertOnConflictDoNothing(
+        table: Table,
+    ) : BatchInsertStatement(table) {
+        override fun prepareSQL(transaction: Transaction) = buildString {
+            append(super.prepareSQL(transaction))
+            append(" ON CONFLICT (id) DO NOTHING")
+        }
+    }
+
+    @Test fun `batch insert number of inserted rows is accurate`() {
+        val tab = object : Table("tab") {
+            val id = varchar("id", 10).uniqueIndex()
+        }
+
+        withTables(TestDB.allH2TestDB + listOf(TestDB.MYSQL), tab) {
+            tab.insert { it[id] = "foo" }
+
+            val numInserted = BatchInsertOnConflictDoNothing(tab).run {
+                addBatch()
+                this[tab.id] = "foo"
+
+                addBatch()
+                this[tab.id] = "bar"
+
+                execute(this@withTables)
+            }
+
+            assertEquals(1, numInserted)
+        }
+    }
 }