EF的连表查询Lambda表达式和linq语句

时间:2022-07-25 18:46:41
var lst = from c in db.Blogs join p in db.Posts on c.Id equals p.BlogId where p.Id==1 select c;
var lst1 = db.Blogs.Join(db.Posts.Where(p=>p.Id==1), b=> b.Id, p=> p.BlogId, (b, p) => new {b});
 public class Blog
 {
    public int Id { get; set; }
    public string Title { get; set; }
 }


 public class Post
 {
    public int Id { get; set; }
    public string Title { get; set; }
    public int BlogId { get; set; } 
 }

 

 

        public List<CommentsViewModel> GetCommentsByPid(int pid, int uid)
        {
            var query = from a in db.Photos
                        join b in db.Comments on a.PID equals b.PID
                        join c in db.Users on b.UID equals c.UID
                        where a.PID == pid
                        select new CommentsViewModel { Id = b.ID, Author = c.UserName, Comment = b.Content, UserAvatar = c.HeadPic, CanDelete = uid == b.UID ? true : false, CanReplay = true, TempDate = b.CreateTime, ParentId = b.ParentId };
            var ret = query.ToList();
            return ret;

//或者
var data = db.Photos. Join(db.Comments, p => p.PID, c => c.PID, (p, c) => new { p, c }). Join(db.Users, n => n.c.UID, u => u.UID, (n, u) => new { n, u }) .Where(m => m.n.p.PID == pid) .Select(m => new CommentsViewModel { Id = m.n.c.ID, Author = m.u.UserName, Comment =m.n.c.Content, }); return data.ToList(); }