Use USING CAST(...) clause when editing Postgres column type.

Author: rspeele

src/Rezoom.SQL.Compiler/AST.fs

@@ -43,6 +43,10 @@ type TypeName =
     | BooleanTypeName
     | DateTimeTypeName
     | DateTimeOffsetTypeName
+    member this.SupportsCollation =
+        match this with
+        | StringTypeName _ -> true
+        | _ -> false
     override this.ToString() =
         match this with
         | GuidTypeName -> "GUID"

src/Rezoom.SQL.Compiler/Postgres.fs

@@ -108,19 +108,30 @@ type private PostgresStatement(indexer : IParameterIndexer) as this =
                 this.Expr.Name(col)
                 ws
             |]
-        let inline changeType (col : Name) (ty : TypeName) (collation : Name option) =
+        let inline changeType (col : Name) (ty : TypeName) (collation : Name option) changingType =
             seq {
                 yield! alterColumn col
                 yield text "TYPE"
                 yield ws
                 yield! this.Expr.TypeName(ty)
                 match collation with
-                | None -> ()
-                | Some collation ->
+                | Some collation when ty.SupportsCollation ->
                     yield ws
                     yield text "COLLATE"
                     yield ws
                     yield this.Expr.CollationName(collation)
+                | _ -> ()
+                if changingType then
+                    yield ws
+                    yield text "USING"
+                    yield ws
+                    yield text "CAST("
+                    yield this.Expr.Name(col)
+                    yield ws
+                    yield text "AS"
+                    yield ws
+                    yield! this.Expr.TypeName(ty)
+                    yield text ")"
             }
         seq {
             yield text "ALTER TABLE"
@@ -165,10 +176,10 @@ type private PostgresStatement(indexer : IParameterIndexer) as this =
                 yield text (if change.NewNullable then "DROP NOT NULL" else "SET NOT NULL")
             | ChangeType change ->
                 let schemaColumn = change.ExistingInfo.Column |> Option.get
-                yield! changeType change.Column change.NewType schemaColumn.Collation
+                yield! changeType change.Column change.NewType schemaColumn.Collation true
             | ChangeCollation change ->
                 let schemaColumn = change.ExistingInfo.Column |> Option.get
-                yield! changeType change.Column schemaColumn.ColumnTypeName (Some change.NewCollation)
+                yield! changeType change.Column schemaColumn.ColumnTypeName (Some change.NewCollation) false
         }
     override this.PrimaryKeyClause(pk) =
         seq {

src/Rezoom.SQL.Test/TestPostgresSmoke.fs

@@ -125,7 +125,7 @@ ALTER TABLE "public"."smoketable1" ALTER COLUMN "float64column" DROP DEFAULT;
 ALTER TABLE "smoketable1" ALTER COLUMN "stringncolumn" TYPE VARCHAR(80) COLLATE "C";
 ALTER TABLE "smoketable1" ALTER COLUMN "float64column" DROP NOT NULL;
 ALTER TABLE "smoketable1" ALTER COLUMN "float64column" SET NOT NULL;
-ALTER TABLE "smoketable1" ALTER COLUMN "int16column" TYPE INT;
+ALTER TABLE "smoketable1" ALTER COLUMN "int16column" TYPE INT USING CAST("int16column" AS INT);
 DROP INDEX "ix_smoketable2_parentid";
 ALTER TABLE "smoketable2" DROP CONSTRAINT "smoketable2_friendid_fk_smoketablefriend_autocolumn" RESTRICT;
 ALTER TABLE "smoketable2" DROP COLUMN "friendid" RESTRICT;