Proper way to compare request with entity

Question

I have issue with implementation Get method into my manager class. How do i need to filter and where i need to write filter method.

In short - i have data class Gym, repository class and method Find in it. I wrote methods in data classes - IsAppreciateToRequest(RequestName) to do smth like this in manager class

public IEnumerable<GymDto> GetGyms(GetGymRequest request)
{
    return _gymRepository
           .Find(gym => gym.IsAppreciateToRequest(request))
           .AsEnumerable()
           .Select(GymDto.FromEntityToDto);
}

I think this is shitcode, but also idk how to get rid of this and how to write it proper way(before this i had Get method like 30-50 lines longer in every manager class)

IsAppreciateToRequest method:

 public bool IsAppreciateToRequest(GetGymRequest other)
        {
            return (string.IsNullOrEmpty(other.Name) || Name == other.Name)
                   &&  (string.IsNullOrEmpty(other.Location) || Location == other.Location) 
                   && (other.SectionRequest == null || Sections.All(section => section.IsAppreciateToRequest(other.SectionRequest)));
        }

Show `IsAppreciateToRequest` method body. Maybe we can inject it into filter. — Svyatoslav Danyliv, Jun 07 '22 at 07:35
The problem is about placing code in right place - i think it`s must be not in data class but idk where it must to be( — Red Star, Jun 07 '22 at 15:33
`IsAppreciateToRequest` is member of which class? And are you ready to use third party extensions? — Svyatoslav Danyliv, Jun 07 '22 at 15:46
IsAppreciateToRequest is a member of every data class i using in my app. This method called while i make filter request. Yes, i`m open to using third party extensions — Red Star, Jun 07 '22 at 20:38

Svyatoslav Danyliv · Accepted Answer · 2022-06-09T08:24:25.387

You can use LINQKit for injecting Expression Tree into filters. It is needed to configure DbContextOptions:

builder
    .UseSqlServer(connectionString) // or any other provider
    .WithExpressionExpanding();     // enabling LINQKit extension

Your classes should be extended with static function which returns Expression<Func<>> and current methods should have ExpandableAttribute

For example:

public class Gym
{
    [Expandable(nameof(IsAppreciateToRequestImpl))]
    public bool IsAppreciateToRequest(GetGymRequest other)
    {
        return (string.IsNullOrEmpty(other.Name) || Name == other.Name)
                && (string.IsNullOrEmpty(other.Location) || Location == other.Location) 
                && (other.SectionRequest == null || Sections.All(section => section.IsAppreciateToRequest(other.SectionRequest)));
    }

    private static Expression<Func<Gym, GetGymRequest, bool>> IsAppreciateToRequestImpl()
    {
        // first parameter is current object
        return (gym, other) => (string.IsNullOrEmpty(other.Name) || gym.Name == other.Name)
                && (string.IsNullOrEmpty(other.Location) || gym.Location == other.Location) 
                && (other.SectionRequest == null || gym.Sections.All(section => section.IsAppreciateToRequest(other.SectionRequest)));
    }
}

// the same technique as in Gym class
public class Section
{
    [Expandable(nameof(IsAppreciateToRequestImpl))]
    public bool IsAppreciateToRequest(GetSectionRequest other)
    {
        return // unknown;
    }

    private static Expression<Func<Section, GetSectionRequest, bool>> IsAppreciateToRequestImpl()
    {
        // first parameter is current object
        return (section, other) => // unknown;
    }
}

Then LINQKit will expand expressions returned by your static methods and will inject conditions into predicate.

The same approach can be used for projecting entity to DTO. Similar my answer here, which also shows known alternatives for LINQKit.

Proper way to compare request with entity

1 Answers1