public static bool TrySplitColumnConstant(this ExpressionOperator expression,
out DbQuery.ColumnOperand column, out DbQuery.ConstantOperand constant)
{
column = null;
constant = null;
if (expression == null)
{
return(false);
}
//try first with left
if ((column = expression.Left as DbQuery.ColumnOperand) == null)
{
if ((column = expression.Right as DbQuery.ColumnOperand) != null)
{
constant = expression.Left as DbQuery.ConstantOperand;
}
}
else
{
constant = expression.Right as DbQuery.ConstantOperand;
}
return(column != null && constant != null);
}
internal DbQueryExpressionExecuter(DbQueryHandler handler,
DbQuery.ColumnOperand columnOperand, TokenType oper, DbQuery.ConstantOperand constantOperand)
{
if (columnOperand == null || !(Operator = oper).IsComparison() || constantOperand == null ||
(Handler = handler) == null)
{
throw new ArgumentException($"cannot execute comparison expression");
}
//get the table column handler
Column = handler.Database.Index(columnOperand.Column.Hash);
// . handler.WhereColumns[columnOperand.Column.Hash];
//get the constant value to compare
Constant = constantOperand.Evaluate(null);
Reader = Handler.TableReaders.FirstOrDefault(r => r.Table == Column.Table);
if (Reader == null)
{
throw new ArgumentException($"could not resolve data table reader for column: {Column}");
}
}
/// <summary>
/// call generic class
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="handler"></param>
/// <param name="columnOperand"></param>
/// <param name="oper"></param>
/// <param name="constantOperand"></param>
/// <returns></returns>
IEnumerable <int> ExecuteColumnExpression <T>(DbQueryHandler handler,
DbQuery.ColumnOperand columnOperand, TokenType oper, DbQuery.ConstantOperand constantOperand)
where T : IComparable <T>
{
var executer = new DbQueryExpressionExecuter <T>(handler, columnOperand, oper, constantOperand);
return(executer.Execute().SelectMany(pair => pair.Value));
}