ABP-多表连接查询

前言：什么是多表连接查询

 

一：编写多表查询语句--内连接

对应SQL语句：

select * from Person  join Telephone on Person.Id = Telephone.PersonId

 

第一种方式：LINQ语法

 public List GetTwo()
        {
            var query = from a in   _entityRepository.GetAll()
                        join b in _TelRepository.GetAll()
                        on a.Id equals b.PersonId
                        select new Twotable{
                            Name=a.Name,
                            Telephone=b.PhoneNumber
                        };
            return query.ToList();
        }

第二种方式：Lambda语法

 public List GetTwo()
        {
            var query = _entityRepository.GetAll()
        .Join(
                _TelRepository.GetAll(),
        top => top.Id,
        art => art.PersonId,
        (top, art) => new Twotable
        {
            Name = top.Name,
            Telephone = art.PhoneNumber
        });
            return query.ToList();
        }

二：编写多表连接查询--左右连接

左连接的概念：

对应SQL语句：

select * from Person  left join Telephone on Person.Id = Telephone.PersonId

 

右连接的概念：

对应SQL语句：

select * from Person  right join Telephone on Person.Id = Telephone.PersonId

多表查询

左右连接，取决于 a b2个的位置 

方法1：LINQ语法

var leftOuterJoin = from a in _entityRepository.GetAll()
                       join b in _TelRepository.GetAll()
                        on a.Id equals b.PersonId
                        into cls from c in cls.DefaultIfEmpty()
                        select new Twotable
                        {
                            Name = a.Name,
                            Telephone = c.PhoneNumber
                        };

方法2：Lambda语法

       var leftOuterJoin = _entityRepository.GetAll()
      .GroupJoin(
              _TelRepository.GetAll(),
      top => top.Id,
      art => art.PersonId,
      (top, art) => new Twotable
      {
          Id = top.Id,
          Name = top.Name,
          Telephone =  art.FirstOrDefault(x => x.PersonId == top.Id).PhoneNumber

      }).Select(o => o);

三：编写多表连接查询---全连接

全连接的概念

对应SQL语句

select * from Person full outer join Telephone on Person.Id = Telephone.PersonId

使用全连接：（合并左右连接就可以了）

      //右连接
            var rightOuterJoin = from b in _TelRepository.GetAll()
                        join a in _entityRepository.GetAll()

                          on b.PersonId equals a.Id
                          into cls
                        from c in cls.DefaultIfEmpty()
                        select new Twotable
                        {
                            Id = c.Id,
                            Name = c.Name,
                            Telephone = b.PhoneNumber
                        };
     //左连接

           var leftOuterJoin = from a in _entityRepository.GetAll()
                        join b in _TelRepository.GetAll()
                        on a.Id equals b.PersonId
                        into cls from c in cls.DefaultIfEmpty()
                        select new Twotable
                        {
                            Name = a.Name,
                            Telephone = c.PhoneNumber
                        };

 

var fullOuterJoin = leftOuterJoin.Union(rightOuterJoin);

或者

var fullOuterJoin = leftOuterJoin.Concat(rightOuterJoin);

番外： 

如果想 3表 或 4表 连接，那就和SQL语句一样在下面加 join就好了

     var query = from b in _TelRepository.GetAll()
                        join a in _entityRepository.GetAll()
                          on b.PersonId equals a.Id
                          into cls
                        from c in cls.DefaultIfEmpty()

                          join d in _userRepository.GetAll()
                           on c.Id equals  d.Id
                            from e in cls.DefaultIfEmpty()

                        select new Twotable
                        {
                            Id = c.Id,
                            //Name = c.Name,
                            Name =e.Name,
                            Telephone = b.PhoneNumber
                        };