1、读取用户和部门两个表的左连接：
var sg = db.Users.GroupJoin(db.Departments, u => u.DepartmentId, d => d.DepartmentId, (u,d) => new { u, d }).Select(o=>o).ToList();
注意：上面将返回所用用户信息和对应的部门信息（即用户部门ID信息缺少，那么用户列表也会显示）
2、读取指定返回列表字段的左连接信息：
var GJoinList = db.Sys_User.GroupJoin(db.Sys_Department, u => u.DepartmentId, d => d.DepartmentId, (u,d) => new { UserId=u.UserId, Account=u.Account, RealName=u.RealName, EnabledMark=u.EnabledMark, DeleteMark=u.DeleteMark,DepartmentName = d.FirstOrDefault(x=>x.DepartmentId==u.DepartmentId).FullName}).Select(o=>o);
3、读取连接表：
var sg = db.Users.Join(db.Departments, u => u.DepartmentId, d => d.DepartmentId, (u,d) => new { u, d }).Select(o=>o).ToList();
注意：这里将只显示用户里DepartmentId和部门表里DepartmentId相等的信息，如果用户没有部门ID则此条用户信息不会显示
var data = db.CRM_OrderDetails.Join(db.CRM_Order, d => d.OrderId, o => o.OrderId, (d, o) => new { d, o }).Select(p => new ProductsListModel() { OrderId =p.o.OrderId, OrderCode=p.o.OrderCode, CustomerName=p.o.CustomerName, ProductName=p.d.ProductName, UnitId=p.d.UnitId, Qty=p.d.Qty, Price=p.d.Price, Amount=p.d.Amount, TaxAmount=p.d.TaxAmount, TaxCostAmount=p.d.TaxCostAmount, CreateTime=p.d.CreateTime, EndTime=p.d.EndTime, Description=p.d.Description }).Where(expression).OrderBy(orderbyExpression);
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