How to intersect two different object collections by specific property?-CodePudding

There are two different objects.

UserDto.cs

public Guid GradeId { get; set; }
public bool isActiveUser { get; set; }

User.cs

public Guid GradeId { get; set; }
public bool isActiveUser { get; set; }
public Guid ParentUserId { get; set; }

Both object have some data and I am trying to get intersection and update only those objects in DB.

var toBeUpdated = userDtos
  .Intersect(mapper.Map<List<User>>(users)) //USING AutoMapper here
  .ToList();


foreach (var item in toBeUpdated)
{
     userRepository.Update(item);
}

These objects must be intersected with GradeId. With the code I wrote, I am not getting any objects by that query. Example :

users :

GradeId - 1 isActive - false

userDtos :

GradId - 1 isActive - true

I want to be able to intersect these two collections by GradeId and set isActive to true(as in DTO)

CodePudding user response：

There are several ways how this can be done. The most intuitive way to find intersections of collections is to iterate over both collections in a double loop:

foreach (var dto in userDtos)
{
    foreach (var user in users)
    {
        if (user.GradeId == dto.GradeId)
        {
            // Do something work here...
            userRepository.Update(user);
        }
    }
}

You can also do the same using Linq:

IEnumerable<User> usersToUpdate =
        from dto to userDtos
        from user to users
        where user.GradeId == dto.GradeId
        select user;

foreach (var user in usersToUpdate)
{
    // Do something work here...
    userRepository.Update(user);
}

Or like this:

IEnumerable<User> usersToUpdate = userDtos
    .SelectMany(dto => users, (dto, user) => new { dto, user })
    .Where(pair => pair.user.GradeId == pair.dto.GradeId)
    .Select(pair => pair.user);

foreach (var user in usersToUpdate)
{
    // Do something work here...
    userRepository.Update(user);
}

CodePudding user response：

There is no need to use nested Foreach.

var items = userDtos.Select(x => x.GradeId)
                          .Intersect(users.Select(y => y.GradeId))
                          .ToList();