如何在实体框架中执行左外连接而不使用查询语法

通常可以通过访问查询的Expression属性从任何查询表达式中获得使用的确切表达式。然后分析那个表达式并复制它。

var expr = products.Expression;

另一方面，使用查询语法的每个表达式都有一个直接的翻译。与into部分连接的子句对应GroupJoin()，而额外的from子句对应SelectMany()。这应该会产生一个等价的查询:

var products = context.Products.GroupJoin(context.TopSellings,
        p => p.Id, t => t.Id, (p, g) => new { p, g })
    .SelectMany(x => x.g.DefaultIfEmpty(),
        (x, tps) => new { x.p, x.g, tps })
    .OrderByDescending(x => x.tps.Rating)
    .Select(x => new { x.p.Name, Rating = x.tps.Rating == null ? 0 : x.tps.Rating });

但是您可以删除一些冗余，删除不再使用的变量，并利用一些有用的操作符。只是要注意，它可能会影响实际产生的查询，所以它不完全匹配，但它应该足够接近。

var products = context.Products.GroupJoin(context.TopSellings,
    p => p.Id, t => t.Id,
    (p, g) => g.DefaultIfEmpty()
        .OrderByDescending(tps => tps.Rating)
        .Select(tps => new { p.Name, Rating = tps.Rating ?? 0 })
);

using EF
 AAWSADBEntitiesContext = new AAWSA_DBEntitiesContext();
        //    .Where(pp1 => ((zemechaObj.DriverId == pp1.DriverId) || (zemechaObj.DriverId == pp1.DriverId)))
        var myresult =( from zemechaObj in AAWSADBEntitiesContext.WaterSupplyForwardedZemechResourses
                        where zemechaObj.CompanyId == companyId && zemechaObj.Status == WaterSupplyServiceRequest.Shared.ToString()
                        from driverObj in AAWSADBEntitiesContext.tbl_Driver
                               .Where(driver => ((zemechaObj.DriverId == driver.DriverId) ))
                                 .DefaultIfEmpty()
                            //fromBranch
                        from fromBranch in AAWSADBEntitiesContext.tbl_CompanyRegistrationInformation
                              .Where(fromB => ((zemechaObj.FromBranchId == fromB.CompanyId)))
                            //toBranch
                        from toBranch in AAWSADBEntitiesContext.tbl_CompanyRegistrationInformation
                              .Where(toB => ((zemechaObj.ToBranchId == toB.CompanyId)))
                                //vehicle
                             from vehicleObj in AAWSADBEntitiesContext.tbl_Vehicle
                                .Where(veh => ((zemechaObj.VehicleId == veh.VehicleId)))
                                  .DefaultIfEmpty()
                                 //assistant one
                        from DriverAssistantOneObj in AAWSADBEntitiesContext.tbl_DriverAssistant
                               .Where(driverAssistOne => ((zemechaObj.DriverAssitantFirstID == driverAssistOne.DriverAssistantId)))
                                 .DefaultIfEmpty()
                            //assistant one
                        from DriverAssistantTwoObj in AAWSADBEntitiesContext.tbl_DriverAssistant
                               .Where(driverAssistTwo=> ((zemechaObj.DriverAssitantSecondID == driverAssistTwo.DriverAssistantId)))
                                 .DefaultIfEmpty()
                            select new BranchResourceForZemechaEntities()
                            {
                                ForwaredResourseID = zemechaObj.ForwaredResourseID,
                                ServiceStartDate = zemechaObj.ServiceStartDate.ToString(),
                                ServiceEndDate = zemechaObj.ServiceEndDate.ToString(),
                                ForwaredDate = zemechaObj.ForwaredDate.ToString(),
                                Status = zemechaObj.Status,
                                Comment = zemechaObj.Comment,
                                //from Branch
                                FromBranchName = fromBranch.CompanyName,
                                //To Branch
                                ToBranchName = toBranch.CompanyName,
                                VehicleId = zemechaObj.VehicleId,
                                //Vehicle info
                                PlateNumber = vehicleObj.PlateNumber+" ",
                                DriverId = zemechaObj.DriverId,
                                //Driver Full Name
                                DriverFullName = driverObj.FirstName + " " + driverObj.MiddleName + " " + driverObj.LastName,
                                // Driver Assitant one Full Name
                                DriverAssitantFirstID = zemechaObj.DriverAssitantFirstID,
                                DriverAssistantOneFullName = DriverAssistantOneObj.FirstName + " " + DriverAssistantOneObj.MiddleName + " " + DriverAssistantOneObj.LastName,
                                // Driver Assitant Two Full Name
                                DriverAssitantSecondID = zemechaObj.DriverAssitantSecondID,
                                DriverAssistantTwoFullName = DriverAssistantTwoObj.FirstName + " " + DriverAssistantTwoObj.MiddleName + " " + DriverAssistantTwoObj.LastName,
                                CompanyId = zemechaObj.CompanyId,
                                FromBranchId = zemechaObj.FromBranchId,
                                ToBranchId = zemechaObj.ToBranchId,
                                BrLoggedUserId = zemechaObj.BrLoggedUserId.ToString()
                            }).ToList();
        return myresult.ToList<BranchResourceForZemechaEntities>();