feat: Add support for changing default value in SQL Server

When creating a column with a DEFAULT value in SQL Server, a DEFAULT constraint is created under the hood. To modify the default value of a column, the constraint has to be dropped first. To do that, the name of the constraint is needed. To be able to obtain its name easily, the way the DEFAULT constraint is created was modified to give it an explicit name with the format DF_TableName_ColumnName. So when adding a new DEFAULT value to a column or modifying an existing one, it's necessary to drop the existing DEFAULT constraint first, and then add a new one.
JetBrains · Aug 7, 2023 · ccf3b1b · ccf3b1b
1 parent f732f99
commit ccf3b1b
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Showing 3 changed files with 42 additions and 9 deletions.
diff --git a/exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Column.kt b/exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/Column.kt
@@ -3,6 +3,7 @@ package org.jetbrains.exposed.sql
 import org.jetbrains.exposed.exceptions.throwUnsupportedException
 import org.jetbrains.exposed.sql.transactions.TransactionManager
 import org.jetbrains.exposed.sql.vendors.H2Dialect
+import org.jetbrains.exposed.sql.vendors.SQLServerDialect
 import org.jetbrains.exposed.sql.vendors.SQLiteDialect
 import org.jetbrains.exposed.sql.vendors.currentDialect
 import org.jetbrains.exposed.sql.vendors.inProperCase
@@ -85,7 +86,8 @@ class Column<T>(
     fun descriptionDdl(modify: Boolean = false): String = buildString {
         val tr = TransactionManager.current()
         val column = this@Column
-        append(tr.identity(column))
+        val columnName = tr.identity(column)
+        append(columnName)
         append(" ")
         val isPKColumn = table.primaryKey?.columns?.contains(column) == true
         val isSQLiteAutoIncColumn = currentDialect is SQLiteDialect && columnType.isAutoInc
@@ -112,7 +114,13 @@ class Column<T>(
                 }
                 exposedLogger.error("${currentDialect.name} ${tr.db.version} doesn't support expression '$expressionSQL' as default value.$clientDefault")
             } else {
-                append(" DEFAULT $expressionSQL")
+                if (currentDialect is SQLServerDialect) {
+                    // Create a DEFAULT constraint with an explicit name to facilitate removing it later if needed
+                    val tableName = tr.identity(column.table)
+                    append(" CONSTRAINT DF_${tableName}_$columnName DEFAULT $expressionSQL")
+                } else {
+                    append(" DEFAULT $expressionSQL")
+                }
             }
         }
 

diff --git a/exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/vendors/SQLServerDialect.kt b/exposed-core/src/main/kotlin/org/jetbrains/exposed/sql/vendors/SQLServerDialect.kt
@@ -251,9 +251,29 @@ open class SQLServerDialect : VendorDialect(dialectName, SQLServerDataTypeProvid
         return columnDefault !in nonAcceptableDefaults
     }
 
-    // EXPOSED-85 Fix changing default value on column in SQL Server as it requires to drop/create constraint
     override fun modifyColumn(column: Column<*>, columnDiff: ColumnDiff): List<String> =
-        super.modifyColumn(column, columnDiff).map { it.replace("MODIFY COLUMN", "ALTER COLUMN") }
+        super.modifyColumn(column, columnDiff).map { statement ->
+            if (columnDiff.defaults) {
+                val transaction = TransactionManager.current()
+                val tableName = transaction.identity(column.table)
+                val colName = transaction.identity(column)
+
+                val dropConstraint = "DROP CONSTRAINT IF EXISTS DF_${tableName}_$colName"
+
+                column.dbDefaultValue?.let {
+                    buildString {
+                        append(statement.substringBefore("MODIFY COLUMN") + dropConstraint)
+                        append("; ")
+                        append(
+                            statement.substringBefore("MODIFY COLUMN") +
+                                "ADD CONSTRAINT DF_${tableName}_$colName DEFAULT ${SQLServerDataTypeProvider.processForDefaultValue(it)} for $colName"
+                        )
+                    }
+                } ?: (statement.substringBefore("MODIFY COLUMN") + dropConstraint)
+            } else {
+                statement.replace("MODIFY COLUMN", "ALTER COLUMN")
+            }
+        }
 
     override fun createDatabase(name: String): String = "CREATE DATABASE ${name.inProperCase()}"
 
@@ -284,7 +304,13 @@ open class SQLServerDialect : VendorDialect(dialectName, SQLServerDataTypeProvid
         return super.createIndex(index)
     }
 
-    override fun createIndexWithType(name: String, table: String, columns: String, type: String, filterCondition: String): String {
+    override fun createIndexWithType(
+        name: String,
+        table: String,
+        columns: String,
+        type: String,
+        filterCondition: String
+    ): String {
         return "CREATE $type INDEX $name ON $table $columns$filterCondition"
     }
 

diff --git a/...t/kotlin/org/jetbrains/exposed/sql/tests/shared/ddl/CreateMissingTablesAndColumnsTests.kt b/...t/kotlin/org/jetbrains/exposed/sql/tests/shared/ddl/CreateMissingTablesAndColumnsTests.kt
@@ -355,9 +355,8 @@ class CreateMissingTablesAndColumnsTests : DatabaseTestsBase() {
                     val actual = SchemaUtils.statementsRequiredToActualizeScheme(emptyTable)
                     assertEquals(1, actual.size)
 
-                    // SQL Server requires drop/create constraint to change defaults, unsupported for now
                     // Oracle treat '' as NULL column and can't alter from NULL to NULL
-                    if (testDb !in listOf(TestDB.SQLSERVER, TestDB.ORACLE)) {
+                    if (testDb != TestDB.ORACLE) {
                         // Apply changes
                         actual.forEach { exec(it) }
                     } else {
@@ -399,8 +398,8 @@ class CreateMissingTablesAndColumnsTests : DatabaseTestsBase() {
             override val primaryKey = PrimaryKey(id)
         }
 
-        val excludeSettings = listOf(TestDB.SQLITE, TestDB.SQLSERVER)
-        val complexAlterTable = listOf(TestDB.POSTGRESQL, TestDB.POSTGRESQLNG, TestDB.ORACLE, TestDB.H2_PSQL)
+        val excludeSettings = listOf(TestDB.SQLITE)
+        val complexAlterTable = listOf(TestDB.POSTGRESQL, TestDB.POSTGRESQLNG, TestDB.ORACLE, TestDB.H2_PSQL, TestDB.SQLSERVER)
         withDb(excludeSettings = excludeSettings) { testDb ->
             try {
                 SchemaUtils.createMissingTablesAndColumns(t1)