Dynamic filter with LINQ (EntityFramework) - asp.net

Question

the problem is quite simple. We have some store with many products.
For example each item has fields (and many others):
Height
Weight
Length
Name
Color
Price
We implement some page where we can filter items by range for numbers (like price, length) and string (color).
So, the problem is here:
- we need to allow people to filter items by any of criteria above (color+price, color+length+weight).
The basic approach with predefined SELECT+WHERE is too hard to main.
Is there any other option?
Thank you.

Answer 1

Jonathan is right. I think using if cases would be easiest and would look something like this.
var res = _dbContextorSource.table.Where(x => x.ID > 0); //something to get all of them
//or (x => x.ID >= 0 && x.ID <= 50) if you're showing 50 on a page
if(FirstFilterIsUsed){
res = res.table.Where(x => x.FirstField == FirstFilter);
}
if(SecondFilterIsUsed){
res = res.table.Where(x => x.SecondField == SecondFilter);
}
//etc
I think you could implement a more clean solution that loops through each filter. This is super pseudo but I've used solutions like this.
var filters = GetUserFilters();
foreach(Filter filter in filters){
res = res.table.Where(x => x.GetType().
GetProperty(filter.MatchingName).GetValue(x) == filter.FilterValue);
}
var result = res.ToList();

Answer 2

Common Solution
The most common solution is performing a big if` case. It takes some time to support all your fields but will work great at the end.
However, if you want to do it dynamically, 2 third-party libraries can help you with this
LINQ Dynamic
https://www.nuget.org/packages/System.Linq.Dynamic.Core/
The syntax required is a little bit different from C# but work great. It's the most popular library to do such a thing.
C# Eval Expression
Disclaimer: I'm the owner of the project C# Eval Expression
The library is not free, but you can do pretty much any dynamic LINQ using the same syntax as C#.
So you will be able to build a string to evaluate and the library will do the rest for you.
Here are some example using EF Classic:
https://dotnetfiddle.net/Otm0Aa
https://dotnetfiddle.net/mwTqW7