private IQueryable <TModel> ApplyOperation <TType>(IQueryable <TModel> set, Expression <Func <TModel, TType> > expr, FilterCommand command)
{
return(set.Where(GetPredicate(expr, command)));
}
private Expression <Func <T, bool> > GetPredicate <T, TType>(Expression <Func <T, TType> > expr, FilterCommand command)
{
Expression expression = null;
try
{
switch (command.Operation)
{
case FilterOperation.Equal:
expression = Expression.Equal(expr.Body, GetConvertedParam <TType>(command.Filter));
break;
case FilterOperation.NotEqual:
expression = Expression.NotEqual(expr.Body, GetConvertedParam <TType>(command.Filter));
break;
case FilterOperation.GreaterThan:
expression = Expression.GreaterThan(expr.Body, GetConvertedParam <TType>(command.Filter));
break;
case FilterOperation.LesserThan:
expression = Expression.LessThan(expr.Body, GetConvertedParam <TType>(command.Filter));
break;
case FilterOperation.StartsWith:
expression = Expression.Call(expr.Body, typeof(TType).GetMethod("ToString", new Type[] { }));
expression = Expression.Call(expression, typeof(string).GetMethod("ToLower", new Type[] { }));
expression = Expression.Call(expression, typeof(string).GetMethod("StartsWith", new Type[] { typeof(string) }), Expression.Constant(command.Filter.ToLower()));
break;
case FilterOperation.Contains:
expression = Expression.Call(expr.Body, typeof(TType).GetMethod("ToString", new Type[] { }));
expression = Expression.Call(expression, typeof(string).GetMethod("ToLower", new Type[] { }));
expression = Expression.Call(expression, typeof(string).GetMethod("Contains", new Type[] { typeof(string) }), Expression.Constant(command.Filter.ToLower()));
break;
}
}
catch (FormatException)
{
expression = Expression.Call(expr.Body, typeof(TType).GetMethod("ToString", new Type[] { }));
expression = Expression.Call(expression, typeof(string).GetMethod("ToLower", new Type[] { }));
expression = Expression.Call(expression, typeof(string).GetMethod("StartsWith", new Type[] { typeof(string) }), Expression.Constant(command.Filter.ToLower()));
}
var argParam = expr.Parameters[0];
var lambda = Expression.Lambda <Func <T, bool> >(expression, argParam);
return(lambda);
}
