Placeholder for alter type compatibility checks

Author: tabdulradi

Diff for: troy-schema/src/main/scala/troy/schema/Message.scala

@@ -20,6 +20,7 @@ object Messages {
   case class ColumnAlreadyExists(t: TableName, c: Identifier) extends Message(s"Invalid column name $c because it conflicts with an existing column in table $t")
 
   case class CannotDropPrimaryKeyPart(c: Identifier) extends Message(s"Cannot drop PRIMARY KEY part $c")
+  case class IncompatibleAlterType(c: Identifier, ot: DataType, nt: DataType) extends Message(s"Cannot change $c from type $ot to type $nt: types are incompatible.")
 
   case class PrimaryKeyNotDefined(t: TableName) extends Message(s"CREATE TABLE $t statement has no Primary key defined")
 

Diff for: troy-schema/src/main/scala/troy/schema/SchemaEngine.scala

@@ -188,7 +188,8 @@ case class SchemaEngineImpl(schema: Schema, context: Option[KeyspaceName]) exten
 
   private val noVariables: Result[Seq[DataType]] = V.success(Seq.empty)
 
-  override def +(stmt: DataDefinition) = stmt match {
+  override def +(stmt: DataDefinition) =
+    validations.validate(stmt).map(_ => stmt) flatMap {
       case s: CreateKeyspace => schema.apply(s).map(s => copy(s))
       case s: CreateTable    => schema.apply(enrichWithContext(s)).map(s => copy(s))
       case s: CreateIndex    => schema.apply(enrichWithContext(s)).map(s => copy(s))

Diff for: troy-schema/src/main/scala/troy/schema/validation/AlterColumnIncompatibleTypes.scala

@@ -0,0 +1,24 @@
+package troy.schema.validation
+
+import troy.cql.ast._
+import troy.cql.ast.ddl.Alter.AlterType
+import troy.schema.{ V, Messages, Schema }
+
+class AlterColumnIncompatibleTypes(schema: Schema) extends Validation[DataDefinition] {
+  import DataType._
+  override def rules = {
+    case AlterTable(tableName, AlterType(columnName, newCqlType)) =>
+      schema.getColumns(tableName, Seq(columnName)).map(_.head.dataType).flatMap { oldCqlType =>
+        if (isCompatible(oldCqlType, newCqlType))
+          noMessages
+        else
+          V.error(Messages.IncompatibleAlterType(columnName, oldCqlType, newCqlType))
+      }
+  }
+
+  def isCompatible(oldDT: DataType, newDT: DataType) = oldDT -> newDT match {
+    case (_, Blob) => true
+    // TODO
+    case _         => oldDT == newDT
+  }
+}

Diff for: troy-schema/src/main/scala/troy/schema/validation/Validation.scala

@@ -1,6 +1,6 @@
 package troy.schema.validation
 
-import troy.cql.ast.DataManipulation
+import troy.cql.ast.{ DataDefinition, DataManipulation }
 import troy.schema._
 
 trait Validation[-T] {
@@ -16,7 +16,9 @@ class Validations(schema: Schema, levelConfig: Message => Validations.Level) {
   def validate(statement: DataManipulation): Result[_] =
     validate(dmValidations, statement)
 
-  def adjustMessageLevels(msgs: Iterable[Message]) = {
+  def validate(statement: DataDefinition): Result[_] =
+    validate(ddValidations, statement)
+
   protected[this] def validate[T](validations: Seq[Validation[T]], statement: T): Result[_] =
     V.merge(validations.map(_.validate(statement).flatMap(adjustMessageLevels)))
 
@@ -38,6 +40,10 @@ class Validations(schema: Schema, levelConfig: Message => Validations.Level) {
     new WhereNonPrimaryNoIndex(schema)
   )
 
+  protected[this] val ddValidations = Seq(
+    new AlterColumnIncompatibleTypes(schema)
+  )
+
   protected[this] val emptyResponse: Result[Unit] = V.success(())
 }
 

Diff for: troy-schema/src/test/scala/troy/schema/AlterTableSpec.scala

@@ -82,6 +82,10 @@ class AlterTableSpec extends WordSpec with Matchers {
           .get(parseQuery("SELECT post_title from test.posts;")).get
         row.asInstanceOf[SchemaEngine.Columns].types shouldBe Seq(DataType.Blob)
       }
+
+      "refuse incompatible types" in {
+        alter("ALTER TABLE test.posts ALTER author_name TYPE date;").getError shouldBe Messages.IncompatibleAlterType("author_name", DataType.Text, DataType.Date)
+      }
     }
 
     "adding options" should {