private void createTempTables(SchemaChanges changes, IOutput output)
{
// For any tables with order-sensitivity and fields in different order between current and desired (ignoring fields that only exist in current),
// Create a new table "_nrdo_reorder" using "select (columns in correct order followed by columns to be dropped) from original table into newname"
// Put the table, the fields (with nullability, datatype and identityness as current but in new order) and a PendingReorderTable into current
// For any tables that need their fields reordered, create a copy of the table with the fields in the right order.
foreach (var origTable in TableType.AllFrom(changes.Current))
{
// Tables that don't exist in desired state are to be dropped, they certainly don't need to be reordered!
if (!changes.Desired.Contains(origTable))
{
continue;
}
// Figure out whether a reorder is needed
if (!FieldType.IsFieldReorderNeeded(changes, origTable.Identifier))
{
continue;
}
// Put the fields in order.
// At this point there may be extra fields that are to be dropped but haven't been yet. They need to stick around until
// it's time to drop them, because before statements may rely on them. But we put those ones last (in the order they're currently in).
var fieldsInOrder = from field in FieldType.ChildrenFrom(changes.Current, origTable.Identifier)
let desired = changes.Desired.Get(field)
orderby
desired != null ? desired.State.OrdinalPosition : int.MaxValue,
field.State.OrdinalPosition
select field;
// Construct the state representation that will be used for the new table.
// It inherits all before statements from the original table so that when it's renamed they'll still be there.
// FIXME: This hardcodes the assumption that CreateTableAsSelect preserves field type, nullability and identity-ness, which may or may not be true on other DBs
// FIXME: any other aspects of field state that we add support for (Default values, check constraints...) need to get dropped here.
var tempTable = TableType.Create(origTable.Name + "_nrdo_reorder");
var pendingReorder = PendingReorderTableType.Create(tempTable.Identifier, origTable.Name);
var tempTableFields = from fi in fieldsInOrder.Select((field, index) => new { field, index })
select fi.field
.WithParent(tempTable.Identifier)
.With(s => s.WithOrdinalPosition(fi.index));
var tempTableBefores = from before in BeforeStatementType.ChildrenFrom(changes.Current, origTable.Identifier)
select before.WithParent(tempTable.Identifier);
// Gather all temporary objects into one list to put them into the database together
var tempTableObjects =
new ObjectState[]
{
tempTable,
pendingReorder
}
.Concat(tempTableFields)
.Concat(tempTableBefores);
var sql = changes.SchemaDriver.GetCreateTableAsSelectSql(tempTable.Name,
string.Join(", ", from field in fieldsInOrder select changes.DbDriver.QuoteIdentifier(field.Name)),
changes.DbDriver.QuoteSchemaIdentifier(origTable.Name));
changes.Put(sql, tempTableObjects);
}
}
