I want to give the user the choice of searching by different properties. For instance
[INPUT TEXT] | [SELECT OPTION {ID, NAME, PHONE}] | [SEARCH]
And I would later build my query like this:
repository.Where(lambda-expression)
Where lambda-expression is build from the selected option {ID, NAME, PHONE} (For example: x => x.NAME.Equals(INPUT TEXT))
Is there a way to build the lambda from the Property name perhaps using reflection?
Thanks
You don't build a lambda expression - you build an expression tree. It's not terribly hard, but it takes a little patience. In your sample you'd probably need:
ParameterExpression parameter = Expression.Parameter(typeof(Foo), "x");
Expression property = Expression.Property(parameter, propertyName);
Expression target = Expression.Constant(inputText);
Expression equalsMethod = Expression.Call(property, "Equals", null, target);
Expression<Func<Foo, bool>> lambda =
Expression.Lambda<Func<Foo, bool>>(equalsMethod, parameter);
That's assuming:
FoopropertyNameinputText
Expression.Call which takes a MethodInfo instead of a string to identify the method.For that sort of thing, I use something like this (note: does a Where "Like") :
public static IQueryable<TEntity> Where<TEntity>(this IQueryable<TEntity> source, string propertyName, string value)
{
Expression<Func<TEntity, bool>> whereExpression = x => x.GetType().InvokeMember(propertyName, BindingFlags.GetProperty, null, x, null).ObjectToString().IndexOf(value, StringComparison.InvariantCultureIgnoreCase) >= 0;
return source.Where(whereExpression);
}
I had to face the same sort of problem and the following method resolved my problem perfectly.
PropertyInfo propertyInfoObj = MyClassObject.GetType().GetProperty(PropertyName);
repository.Where(x => propertyInfoObj.GetValue(x) == SearchValue).Select(x => propertyInfoObj.GetValue(x)).FirstOrDefault();
