internal static bool?CanBeNull(SqlExpression expr)
{
switch (expr.NodeType)
{
case SqlNodeType.ExprSet:
SqlExprSet exprSet = (SqlExprSet)expr;
return(CanBeNull(exprSet.Expressions));
case SqlNodeType.SimpleCase:
SqlSimpleCase sc = (SqlSimpleCase)expr;
return(CanBeNull(sc.Whens.Select(w => w.Value)));
case SqlNodeType.Column:
SqlColumn col = (SqlColumn)expr;
if (col.MetaMember != null)
{
return(col.MetaMember.CanBeNull);
}
else if (col.Expression != null)
{
return(CanBeNull(col.Expression));
}
return(null); // Don't know.
case SqlNodeType.ColumnRef:
SqlColumnRef cref = (SqlColumnRef)expr;
return(CanBeNull(cref.Column));
case SqlNodeType.Value:
return(((SqlValue)expr).Value == null);
case SqlNodeType.New:
case SqlNodeType.Multiset:
case SqlNodeType.Grouping:
case SqlNodeType.DiscriminatedType:
case SqlNodeType.IsNotNull: // IsNull\IsNotNull always return true or false and can never return NULL.
case SqlNodeType.IsNull:
case SqlNodeType.Exists:
return(false);
case SqlNodeType.Add:
case SqlNodeType.Sub:
case SqlNodeType.Mul:
case SqlNodeType.Div:
case SqlNodeType.Mod:
case SqlNodeType.BitAnd:
case SqlNodeType.BitOr:
case SqlNodeType.BitXor:
case SqlNodeType.Concat: {
SqlBinary bop = (SqlBinary)expr;
bool? left = CanBeNull(bop.Left);
bool? right = CanBeNull(bop.Right);
return((left != false) || (right != false));
}
case SqlNodeType.Negate:
case SqlNodeType.BitNot: {
SqlUnary uop = (SqlUnary)expr;
return(CanBeNull(uop.Operand));
}
case SqlNodeType.Lift: {
SqlLift lift = (SqlLift)expr;
return(CanBeNull(lift.Expression));
}
case SqlNodeType.OuterJoinedValue:
return(true);
default:
return(null); // Don't know.
}
}
internal virtual SqlExpression VisitLift(SqlLift lift)
{
lift.Expression = this.VisitExpression(lift.Expression);
return(lift);
}
internal override SqlExpression VisitLift(SqlLift lift)
{
return(new SqlLift(lift.ClrType, this.VisitExpression(lift.Expression), lift.SourceExpression));
}
internal override SqlExpression VisitLift(SqlLift lift)
{
lift.Expression = base.VisitExpression(lift.Expression);
return(lift);
}
internal override SqlExpression VisitLift(SqlLift lift) => new SqlLift(lift.ClrType, VisitExpression(lift.Expression), lift.SourceExpression);
