实体框架Linq查询何时命中Sql Databse？

Question

i'm new in entity framework.Below is my code,

So in my code i have created object of my db context and then i have a query 'queryForAuthentication' and in that i have used two tables 'conDb.SystemMasters' and joined with conDb.SystemAdminMasters , so will hit twice or how does it manage . i want to know when does entity framework will hit in to database ?

 QuizzrEntities conDb = new QuizzrEntities();
 List<OnLoginData> lstOnLogoonData = new List<OnLoginData>();
 string userpassWordHash = string.Empty;
 var queryForAuthentication =from systemObj in conDb.SystemMasters
                             where systemObj.StaffPin == dminLoginInput.StaffPin
                             join admin in conDb.SystemAdminMasters on systemObj.SystemId equals admin.SystemID
                             select new 
                            {
                             admin.PasswordSalt,
                             admin.PasswordHash, 
                             systemObj.StaffPin,
                             admin.UserName, 
                             admin.SystemID 
                            };
 if (queryForAuthentication.Count() > 0)
                    {
                        CheckStaffPin = true;
                        var GetUserUsingUsernamePasword = queryForAuthentication.Where(u => u.UserName.ToLower() == AdminLoginInput.UserName.ToLower());
                        if (GetUserUsingUsernamePasword.ToList().Count == 1)
                        {
                            checkuserName = true;
                            string DBPasswordSalt = queryForAuthentication.ToList()[0].PasswordSalt,
                                   DBPasswordHash = queryForAuthentication.ToList()[0].PasswordHash,
                                   StaffPin = queryForAuthentication.ToList()[0].StaffPin;
                            userpassWordHash = Common.GetPasswordHash(AdminLoginInput.Password, DBPasswordSalt);
                            if ((DBPasswordHash == userpassWordHash) && (AdminLoginInput.StaffPin.ToLower() == StaffPin.ToLower()))
                            {
                                checkPassword = true;
                                CheckStaffPin = true;
                            }
                            else if (DBPasswordHash == userpassWordHash)
                            {
                                checkPassword = true;
                            }
                            else if (AdminLoginInput.StaffPin.ToLower() == StaffPin.ToLower())
                            {
                                CheckStaffPin = true;
                            }


                        }

                    }

So in my code i have created object of my db context and then i have a query 'queryForAuthentication' and in that i have used two tables 'conDb.SystemMasters' and joined with conDb.SystemAdminMasters , so will hit twice or how does it manage . i want to know when does entity framework will hit in to database ?

Answer 1

It's hits the database whenever you fire a query. And query will be fired whenever you perform ToList, First, FirstOrDefault etc. operation. Till then it only builds the query.

Answer 2

try Code

 QuizzrEntities conDb = new QuizzrEntities();
 List<OnLoginData> lstOnLogoonData = new List<OnLoginData>();
 string userpassWordHash = string.Empty;
 var queryForAuthentication =(from systemObj in conDb.SystemMasters
                         where systemObj.StaffPin == dminLoginInput.StaffPin
                         join admin in conDb.SystemAdminMasters on systemObj.SystemId equals admin.SystemID
                         select new 
                        {
                        PasswordSalt= admin.PasswordSalt,
                        PasswordHash= admin.PasswordHash, 
                        StaffPin= systemObj.StaffPin,
                        UserName= admin.UserName, 
                       SystemID =  admin.SystemID 
                        }).FirstOrDefault();
If(queryForAuthentication !=null)
{
-----------------
-----------------
*****Your Code*******
}

Answer 3

In entity framework also work with sql query based. If you are disconnected using .ToList() then only the record taken from local otherwise it's works as DBQuery. if you check the result view in debug view it's Execute the Query and Return the data.

If you are processing the data is discontinued from the base it's executed finally where you want the result.

You processing data locally then you can disconnect the connection between linq and sql using call .ToList(). it's Processing only one time the Object weight is high more than query.

Answer 4

var queryForAuthentication =from systemObj in conDb.SystemMasters
                         where systemObj.StaffPin == dminLoginInput.StaffPin
                         join admin in conDb.SystemAdminMasters on systemObj.SystemId equals admin.SystemID
                         select new 
                        {
                         admin.PasswordSalt,
                         admin.PasswordHash, 
                         systemObj.StaffPin,
                         admin.UserName, 
                         admin.SystemID 
                        }.ToList() ; // It will fetch the data
//Check from inmemory collection 
if (queryForAuthentication.Count > 0)

//As you already have the data in memory this filter applied against inmemory collection not against database.
var GetUserUsingUsernamePasword = queryForAuthentication
             .Where(u =>u.UserName.ToLower() == AdminLoginInput.UserName.ToLower());