Add support for check constraints. (#270)

* #268 Add support for check constraints.
* Add support for multi-column check constraints
* Fixed error when parsing check constraints
* Improved CHECK constraint support
- Warning shown when trying to create a CHECK constraint in MySQL
- Constraint with names that were already added are ignored and a warning is shown
- White spaces are now trimmed from constraint names
- Improved tests
* Replaced exception with warn log when using on an unsupported database

src/main/kotlin/org/jetbrains/exposed/sql/Column.kt

@@ -85,7 +85,6 @@ class Column<T>(val table: Table, val name: String, override val columnType: ICo
             append(" NOT NULL")
         }
 
-
         if (isOneColumnPK()) {
             append(" PRIMARY KEY")
         }

src/main/kotlin/org/jetbrains/exposed/sql/Constraints.kt

@@ -61,6 +61,37 @@ data class ForeignKeyConstraint(val fkName: String, val refereeTable: String, va
 
 }
 
+data class CheckConstraint(val tableName: String, val checkName: String, val checkOp: String) : DdlAware {
+
+    companion object {
+        fun from(table: Table, name: String, op: Op<Boolean>): CheckConstraint {
+            val tr = TransactionManager.current()
+            return CheckConstraint(tr.identity(table), if (name.isBlank()) "" else tr.quoteIfNecessary(name), op.toString())
+        }
+    }
+
+    internal val checkPart = buildString {
+        if (checkName.isNotBlank()) append(" CONSTRAINT $checkName")
+        append(" CHECK ($checkOp)")
+    }
+
+    override fun createStatement(): List<String> {
+        return if (currentDialect is MysqlDialect) {
+            exposedLogger.warn("Creation of CHECK constraints is not currently supported by MySQL")
+            listOf()
+        } else listOf("ALTER TABLE $tableName ADD$checkPart")
+    }
+
+    override fun dropStatement(): List<String> {
+        return if (currentDialect is MysqlDialect) {
+            exposedLogger.warn("Deletion of CHECK constraints is not currently supported by MySQL")
+            listOf()
+        } else listOf("ALTER TABLE $tableName DROP CONSTRAINT $checkName")
+    }
+
+    override fun modifyStatement() = dropStatement() + createStatement()
+}
+
 data class Index(val columns: List<Column<*>>, val unique: Boolean, val customName: String? = null) : DdlAware {
     val table: Table
 

src/main/kotlin/org/jetbrains/exposed/sql/Table.kt

@@ -154,6 +154,7 @@ open class Table(name: String = ""): ColumnSet(), DdlAware {
     override fun describe(s: Transaction): String = s.identity(this)
 
     val indices = ArrayList<Index>()
+    val checkConstraints = ArrayList<Pair<String, Op<Boolean>>>()
 
     override val fields: List<Expression<*>>
         get() = columns
@@ -418,6 +419,28 @@ open class Table(name: String = ""): ColumnSet(), DdlAware {
         index(customIndexName,true, *columns)
     }
 
+    /**
+     * Creates a check constraint in this column.
+     * @param name The name to identify the constraint, optional. Must be **unique** (case-insensitive) to this table, otherwise, the constraint will
+     * not be created. All names are [trimmed][String.trim], blank names are ignored and the database engine decides the default name.
+     * @param op The expression against which the newly inserted values will be compared.
+     */
+    fun <T> Column<T>.check(name: String = "", op: SqlExpressionBuilder.(Column<T>) -> Op<Boolean>) = apply {
+        table.checkConstraints.takeIf { name.isEmpty() || it.none { it.first.equals(name, true) } }?.add(name to SqlExpressionBuilder.op(this))
+                ?: exposedLogger.warn("A CHECK constraint with name '$name' was ignored because there is already one with that name")
+    }
+
+    /**
+     * Creates a check constraint in this table.
+     * @param name The name to identify the constraint, optional. Must be **unique** (case-insensitive) to this table, otherwise, the constraint will
+     * not be created. All names are [trimmed][String.trim], blank names are ignored and the database engine decides the default name.
+     * @param op The expression against which the newly inserted values will be compared.
+     */
+    fun check(name: String = "", op: SqlExpressionBuilder.() -> Op<Boolean>) {
+        checkConstraints.takeIf { name.isEmpty() || it.none { it.first.equals(name, true) } }?.add(name to SqlExpressionBuilder.op())
+                ?: exposedLogger.warn("A CHECK constraint with name '$name' was ignored because there is already one with that name")
+    }
+
     val ddl: List<String>
         get() = createStatement()
 
@@ -444,6 +467,9 @@ open class Table(name: String = ""): ColumnSet(), DdlAware {
                         append(references.joinToString(prefix = ", ", separator = ", ") { ForeignKeyConstraint.from(it).foreignKeyPart })
                     }
                 }
+                if (checkConstraints.isNotEmpty()) {
+                    append(checkConstraints.joinToString(prefix = ",", separator = ",") { (name, op) -> CheckConstraint.from(this@Table, name, op).checkPart })
+                }
 
                 append(")")
             }

src/test/kotlin/org/jetbrains/exposed/sql/tests/shared/DDLTests.kt

@@ -219,7 +219,7 @@ class DDLTests : DatabaseTestsBase() {
             else -> "NULL"
         }
 
-        
+
         withTables(TestTable) {
             val dtType = currentDialect.dataTypeProvider.dateTimeType()
             assertEquals("CREATE TABLE " + if (currentDialect.supportsIfNotExists) { "IF NOT EXISTS " } else { "" } +
@@ -421,11 +421,11 @@ class DDLTests : DatabaseTestsBase() {
         }
     }
 
-    
+
     private abstract class EntityTable(name: String = "") : IdTable<String>(name) {
         override val id: Column<EntityID<String>> = varchar("id", 64).clientDefault { UUID.randomUUID().toString() }.primaryKey().entityId()
     }
-    
+
     @Test fun complexTest01() {
         val User = object : EntityTable() {
             val name = varchar("name", 255)
@@ -504,6 +504,70 @@ class DDLTests : DatabaseTestsBase() {
             SchemaUtils.drop(missingTable)
         }
     }
+
+    @Test fun testCheckConstraint01() {
+        val checkTable = object : Table("checkTable") {
+            val positive = integer("positive").check { it greaterEq 0 }
+            val negative = integer("negative").check("subZero") { it less 0 }
+        }
+
+        withTables(listOf(TestDB.MYSQL), checkTable) {
+            checkTable.insert {
+                it[positive] = 42
+                it[negative] = -14
+            }
+
+            assertEquals(1, checkTable.selectAll().count())
+
+            assertFailAndRollback("Check constraint 1") {
+                checkTable.insert {
+                    it[positive] = -472
+                    it[negative] = -354
+                }
+            }
+
+            assertFailAndRollback("Check constraint 2") {
+                checkTable.insert {
+                    it[positive] = 538
+                    it[negative] = 915
+                }
+            }
+        }
+    }
+
+    @Test fun testCheckConstraint02() {
+        val checkTable = object : Table("multiCheckTable") {
+            val positive = integer("positive")
+            val negative = integer("negative")
+
+            init {
+                check("multi") { (negative less 0) and (positive greaterEq 0) }
+            }
+        }
+
+        withTables(listOf(TestDB.MYSQL), checkTable) {
+            checkTable.insert {
+                it[positive] = 57
+                it[negative] = -32
+            }
+
+            assertEquals(1, checkTable.selectAll().count())
+
+            assertFailAndRollback("Check constraint 1") {
+                checkTable.insert {
+                    it[positive] = -47
+                    it[negative] = -35
+                }
+            }
+
+            assertFailAndRollback("Check constraint 2") {
+                checkTable.insert {
+                    it[positive] = 53
+                    it[negative] = 91
+                }
+            }
+        }
+    }
 }
 
 private fun String.inProperCase(): String = TransactionManager.currentOrNull()?.let { tm ->