How to get all data from ef core many to many

Question

On EF core have Two tables(Page, Group) both have many to many relations with junction table GroupPage. Want to get all pages data with junction table related data based on groupId as like bellow.

Possible duplicate of [How to create a many to many relationship with latest nightly builds of EF Core?](https://stackoverflow.com/questions/29442493/how-to-create-a-many-to-many-relationship-with-latest-nightly-builds-of-ef-core) — Jan Paolo Go, May 22 '19 at 13:54
https://blog.oneunicorn.com/2017/09/25/many-to-many-relationships-in-ef-core-2-0-part-1-the-basics/ — Jan Paolo Go, May 22 '19 at 13:54

score 0 · Answer 1 · answered May 22 '19 at 08:30

If you construct your EF relation correctly you should not have a GroupPage entity.

See Entity Framework Database First many-to-many on how to construct your EF EDM correctly.

Once you have your EDM correctly mapped, you should have the classes

public class Page
{
    public int Id { get; set; }
    public ICollection<Group> Groups { get; set; }
    ...
}

public class Group
{
    public int Id { get; set; }
    public ICollection<Page> Pages { get; set; }
    ...
}

Then you just need to do the following

public IQueryable<Page> GetPages(int groupId)
{
    return from group in _context.Groups
           where group.Id == groupId
           from page in group.Pages
           select page;
}

score 0 · Answer 2 · answered May 24 '19 at 05:07

The following syntax is self-descriptive. Here are the entities structure and Page Dto.

public class Page
{
    public int Id { get; set; }
    public ICollection<Group> Groups { get; set; }
    ...
}

public class Group
{
    public int Id { get; set; }
    public ICollection<Page> Pages { get; set; }
    ...
}


public class PageGroup
{
    public int PageId { get; set; }
    public Page Page { get; set; }
    public int GroupId { get; set; }
    public Group Group { get; set; }   
}


public class PagesDto 
{
    public string Name { get; set; }
    public int GroupId { get; set; }
    public int PageId { get; set; }
    public string Description { get; set; }
    public string Tab { get; set; }
    public string Module { get; set; }
    public bool? IsActive { get; set; }
    public bool? IsDefault { get; set; }

    public PagesDto()
    {
        IsActive = false;
        IsDefault = false;
    }
}

Following function help us to get group related pages information.

public async Task<List<PagesDto>> GetAllPagesByGroupId(int selectedGroupId)
{
    //get all pages
    var pages = await _pagesRepository.GetAll().Select(p => new PagesDto {
        PageId = p.Id,
        Name = p.Name,
        GroupId = 0

    }).ToListAsync();

    //get group ralated pages
    var selectedGroupPageIds = _groupPagesRepository
        .GetAll()
        .Where(p => p.GroupId == selectedGroupId)
        .Select(p => p.PageId);

    //update page information base on group related pages info.
    foreach (var item in pages.Where(p=>selectedGroupPageIds.Contains(p.PageId)))
    {
        item.GroupId = selectedGroupId;                
    }

    return pages;

}

How to get all data from ef core many to many

2 Answers2