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Converting a given SQL Query to LINQ

I'm new to creating a LINQ so I'm having a hard time converting this SQL query into LINQ. Can someone help me please
SELECT *
FROM myTable1
WHERE (Flag1 <> 'X' OR Flag2 != 'X' OR Flag3 != 'X')
AND number IN (SELECT externalid FROM db2.myTable2 WHERE item = 6)
This is what I've already tried
//get external id
var externalNumber = from s in db2.myTable2
where s.item == 6
select externalid;
var query = from f in db1.myTable1
where (f.Flag1 != "X" || f.Flag2 != "X" || f.Flag3 != "X") && f.number == externalNumber
select f;

Direct translation is:
var query =
from f in db.myTable1
where (f.Flag1 != "X" || f.Flag2 != "X" || f.Flag3 !="X") &&
db.myTable2.Where(s => s.item == 6).Select(s => s.externalId).Contains(f.number)
select f;
IN in LINQ has analogue Contains

var externalid = db2.myTable2Repository.FirstOrDefault(f=>f.item == 2).Result.externalid;
This first code return externalid from db2.myTable2
var data = myTable1Repository.GetAll().Where(w=>(w.Flag1 != X || w.Flag2 != X || w.Flag3 != X) && w.number == externalid)
Second code:
GetAll() is a method of your repository (or baseRepository) and Where() is part of linq
First part of where -> (w.Flag1 != X || w.Flag2 != X || w.Flag3 != X) is self explain
Second part -> (&& w.number == externalid):
I'm not very good with sql so this second part may have got it wrong ,but if I understand correctly, you check the "number" property against a value from another table, so you can just look up this value and store it in a variable.
I'm sorry if I misunderstood the second part in the "and number in", I'm really not good at SQL, and for my bad English too.
If you have any questions we are here :D

Try the Below code:
DatabaseEntities dc=new DatabaseEntities();
var res=dc.myTable1.Where(s=>s.Flag <> 'X' || Flag2 !='X' || Flag3 !='X' && s.number.Contains(dc.myTable2.Where(m=>m.item==6)))

Entity Framework: Count() very slow on large DbSet and complex WHERE clause

I need to perform a count operation on this Entity Framework (EF6) data set using a relatively complex expression as a WHERE clause and expecting it to return about 100k records.
The count operation is obviously where records are materialized and therefore the slowest of operations to take place. The count operation is taking about 10 seconds in our production environment which is unacceptable.
Note that the operation is performed on the DbSet directly (db being the Context class), so no lazy loading should be taking place.
How can I further optimize this query in order to speed up the process?
The main use case is displaying an index page with multiple filter criteria but the the function is also used for writing generic queries to the ParcelOrderstable as required for other operations in the service classes which might be a bad idea resulting in very complex queries resulting from laziness and might potentially be a future problem.
The count is later used for pagination, and a much smaller number of records (e.g. 500) is actually displayed. This is a database-first project using SQL Server.
ParcelOrderSearchModel is a C#-class that serves to encapsualte query parameters and is used exclusively by service classes in order to call the GetMatchingOrdersfunction.
Note that on the majority of calls, the majority of the parameters of ParcelOrderSearchModel will be null.
public List<ParcelOrderDto> GetMatchingOrders(ParcelOrderSearchModel searchModel)
{
// cryptic id known --> allow public access without login
if (String.IsNullOrEmpty(searchModel.KeyApplicationUserId) && searchModel.ExactKey_CrypticID == null)
throw new UnableToCheckPrivilegesException();
Func<ParcelOrder, bool> userPrivilegeValidation = (x => false);
if (searchModel.ExactKey_CrypticID != null)
{
userPrivilegeValidation = (x => true);
}
else if (searchModel.KeyApplicationUserId != null)
userPrivilegeValidation = privilegeService.UserPrivilegeValdationExpression(searchModel.KeyApplicationUserId);
var criteriaMatchValidation = CriteriaMatchValidationExpression(searchModel);
var parcelOrdersWithNoteHistoryPoints = db.HistoryPoint.Where(hp => hp.Type == (int)HistoryPointType.Note)
.Select(hp => hp.ParcelOrderID)
.Distinct();
Func<ParcelOrder, bool> completeExpression = order => userPrivilegeValidation(order) && criteriaMatchValidation(order);
searchModel.PaginationTotalCount = db.ParcelOrder.Count(completeExpression);
// todo: use this count for pagination
}
public Func<ParcelOrder, bool> CriteriaMatchValidationExpression(ParcelOrderSearchModel searchModel)
{
Func<ParcelOrder, bool> expression =
po => po.ID == 1;
expression =
po =>
(searchModel.KeyUploadID == null || po.UploadID == searchModel.KeyUploadID)
&& (searchModel.KeyCustomerID == null || po.CustomerID == searchModel.KeyCustomerID)
&& (searchModel.KeyContainingVendorProvidedId == null || (po.VendorProvidedID != null && searchModel.KeyContainingVendorProvidedId.Contains(po.VendorProvidedID)))
&& (searchModel.ExactKeyReferenceNumber == null || (po.CustomerID + "-" + po.ReferenceNumber) == searchModel.ExactKeyReferenceNumber)
&& (searchModel.ExactKey_CrypticID == null || po.CrypticID == searchModel.ExactKey_CrypticID)
&& (searchModel.ContainsKey_ReferenceNumber == null || (po.CustomerID + "-" + po.ReferenceNumber).Contains(searchModel.ContainsKey_ReferenceNumber))
&& (searchModel.OrKey_Referencenumber_ConsignmentID == null ||
((po.CustomerID + "-" + po.ReferenceNumber).Contains(searchModel.OrKey_Referencenumber_ConsignmentID)
|| (po.VendorProvidedID != null && po.VendorProvidedID.Contains(searchModel.OrKey_Referencenumber_ConsignmentID))))
&& (searchModel.KeyClientName == null || po.Parcel.Name.ToUpper().Contains(searchModel.KeyClientName.ToUpper()))
&& (searchModel.KeyCountries == null || searchModel.KeyCountries.Contains(po.Parcel.City.Country))
&& (searchModel.KeyOrderStates == null || searchModel.KeyOrderStates.Contains(po.State.Value))
&& (searchModel.KeyFromDateRegisteredToOTS == null || po.DateRegisteredToOTS > searchModel.KeyFromDateRegisteredToOTS)
&& (searchModel.KeyToDateRegisteredToOTS == null || po.DateRegisteredToOTS < searchModel.KeyToDateRegisteredToOTS)
&& (searchModel.KeyFromDateDeliveredToVendor == null || po.DateRegisteredToVendor > searchModel.KeyFromDateDeliveredToVendor)
&& (searchModel.KeyToDateDeliveredToVendor == null || po.DateRegisteredToVendor < searchModel.KeyToDateDeliveredToVendor);
return expression;
}
public Func<ParcelOrder, bool> UserPrivilegeValdationExpression(string userId)
{
var roles = GetRolesForUser(userId);
Func<ParcelOrder, bool> expression =
po => po.ID == 1;
if (roles != null)
{
if (roles.Contains("ParcelAdministrator"))
expression =
po => true;
else if (roles.Contains("RegionalAdministrator"))
{
var user = db.AspNetUsers.First(u => u.Id == userId);
if (user.RegionalAdministrator != null)
{
expression =
po => po.HubID == user.RegionalAdministrator.HubID;
}
}
else if (roles.Contains("Customer"))
{
var customerID = db.AspNetUsers.First(u => u.Id == userId).CustomerID;
expression =
po => po.CustomerID == customerID;
}
else
{
expression =
po => false;
}
}
return expression;
}

If you can possibly avoid it, don't count for pagination. Just return the first page. It's always expensive to count and adds little to the user experience.
And in any case you're building the dynamic search wrong.
You're calling IEnumerable.Count(Func<ParcelOrder,bool>), which will force client-side evaluation where you should be calling IQueryable.Count(Expression<Func<ParcelOrder,bool>>). Here:
Func<ParcelOrder, bool> completeExpression = order => userPrivilegeValidation(order) && criteriaMatchValidation(order);
searchModel.PaginationTotalCount = db.ParcelOrder.Count(completeExpression);
But there's a simpler, better pattern for this in EF: just conditionally add criteria to your IQueryable.
eg put a method on your DbContext like this:
public IQueryable<ParcelOrder> SearchParcels(ParcelOrderSearchModel searchModel)
{
var q = this.ParcelOrders();
if (searchModel.KeyUploadID != null)
{
q = q.Where( po => po.UploadID == searchModel.KeyUploadID );
}
if (searchModel.KeyCustomerID != null)
{
q = q.Where( po.CustomerID == searchModel.KeyCustomerID );
}
//. . .
return q;
}

Generic filtering on query string parameters

I'm looking to convert our current API architecture to a more generic query-able structure that doesn't require us to hard card each possible parameter and build up a custom query. Here is an example of what our current architecture looks like,
[HttpGet]
[Route("Companies/{id:int}/Implementations/Tasks")]
public async Task<IApiResponse<List<CompanyIPTDTO>>> GetCompanyIPTs(int? id = null,
int? taskId = null, int? completedById = null, DateTime? dateCompletedStart = null,
DateTime? dateCompletedEnd = null, int page = 1, int? pageSize = null)
{
// Instantiate generic query
Expression<Func<CompanyIPT, bool>> query = null;
// Check parameters and build the lambda query
// Check if the parameter is given and if the query field is already filled so as to either set or add a query
if (id != null && query != null) query = query.And(t => t.CompanyID == id);
else if (id != null && query == null) query = t => t.CompanyID == id;
if (taskId != null && query != null) query = query.And(t => t.ProcessTaskID == taskId);
else if (taskId != null && query == null) query = t => t.ProcessTaskID == taskId;
if (completedById != null && query != null) query = query.And(t => t.CompletedByID == completedById);
else if (completedById != null && query == null) query = t => t.CompletedByID == completedById;
if ((dateCompletedStart != null && dateCompletedEnd != null) && query != null) query = query.And(a => a.DateCompleted >= dateCompletedStart && a.DateCompleted <= dateCompletedEnd);
else if ((dateCompletedStart != null && dateCompletedEnd != null) && query == null) query = a => a.DateCompleted >= dateCompletedStart && a.DateCompleted <= dateCompletedEnd;
// Execute the GET with the appended query and paging information
var result = _uow.CompanyIPTRepository.List(filter: query, page: page, pageSize: pageSize);
int totalPossibleRecords = _uow.CompanyIPTRepository.GetTotalRecords(filter: query);
return new ApiSuccessResponse<List<CompanyIPTDTO>>(HttpStatusCode.OK, result.Select(x => Mapper.Map<CompanyIPTDTO>(x)).ToList(), result.Count(), Request.RequestUri, totalPossibleRecords, pageSize);
}
And as you can see this gets very cumbersome for a large API on every get request to have to customize the query checks. I assume there must be some way to do this generically based on a query string parameter that comes in. For example in this case I would love to see a request come in that looks like,
https://www.example.com/api/Companies/15/Implementations/Tasks?q=[completedById=5,dateCompletedStart=1/15/18,dateCompletedEnd=1/17/18]
And after coming in like this I assume we could build something that uses Reflection to look at the object and verify these fields exist and build up a generic query to hit our DB?
Anyone know where to point us in the right direction?

Search keyword using linq in asp.net with c#back end

List<search> alllist = wsWSemloyee.GetAllProject(); //where search is model class contains properties..
string search_key = "%" + txtsearch.Text.Trim() + "%";
List<search> result = new List<search>();
foreach (search item in alllist)
{
var op = (
from a in alllist
where a.Sfirstname.Contains(search_key) || a.Slastname.Contains(search_key) || a.Smob.Contains(search_key) || a.Scity.Contains(search_key) || a.Sstate.Contains(search_key)
//where SqlMethods.Like(a.Sfirstname,search_key)||SqlMethods.Like(a.Slastname,search_key)||SqlMethods.Like(a.Scity,search_key)||SqlMethods.Like(a.Smob,search_key)||SqlMethods.Like(a.Sstate,search_key)
select a
);
// List<search> lst = op.ToList<search>();
if (op != null)
{
result.Add(item);
}
}
if (result.Count != 0)
{
dgv_searchreport.DataSource = result;
dgv_searchreport.DataBind();// data grid view
}
its not working...
giving all result present in alllist..
//where search is model class contains properties..

I'ts because you are comparing if result of your linq query is not null and then adding variable from foreach clause. When any single item from allproducts will match condition then op will be never null and then whole collection will be contained in result. What you want is probably following:
var result = (from a in alllist
where a.Sfirstname.Contains(search_key)
|| a.Slastname.Contains(search_key)
|| a.Smob.Contains(search_key)
|| a.Scity.Contains(search_key)
|| a.Sstate.Contains(search_key)
select a).ToList();
That will pick all items which match condition and enumerate them to list.

May this helps you..
string search_key = txtsearch.Text.Trim(); // instead "%" + txtsearch.Text.Trim() + "%";
List<search> result = new List<search>();
var op = (from a in alllist
where a.Sfirstname.Contains(search_key) || a.Slastname.Contains(search_key) || ......
select a);
if(op.Count() > 0)
result = op.ToList();

How do I add multiple optional parameters to linq query

I Have to check and add the optional parameter in function but its taking lengthy code to go through IF-Else statement, If I choose switch statement then Cannot convert 'var' variable to string error keep coming up, How do I check and add optional parameters to linq query please help. Here is my code. (I will provide both the one with If statement and other one with switch statement which is throwing error)
Code 1 If-else statement:
public static void loadGrid(ref GridView gvMain, string cID, string desig = "All", string importancy = "All", string status = "All")
{
int _cId = Convert.ToInt32(cID);
List<clsclass> list = new List<clsclass>();
var db = new MyEntities();
if (_cId == 0 && desig == "All" && importancy == "All" && status == "All")
{
var query = from table in db.Members select table;
list.Clear();
foreach (var item in query)
{
clsclass ctl = new clsclass();
ctl.Id = Convert.ToInt32(item.LID);
ctl.Name = item.FirstName + " " + item.LastName;
ctl.Gender = item.Gender;
ctl.Age = Convert.ToInt32(item.Age);
ctl.Mobile = item.Mobile;
ctl.Workphone = item.WorkPhone;
ctl.Designation = item.Designation;
ctl.Importancy = item.Importancy;
list.Add(ctl);
}
}
else if (_cId != 0 && desig == "All" && importancy == "All" && status == "All")
{
var query = from table in db.Members where table.CID == _cId select table;
list.Clear();
foreach (var item in query)
{
clsclass ctl = new clsclass();
ctl.Id = Convert.ToInt32(item.LID);
ctl.Name = item.FirstName + " " + item.LastName;
ctl.Gender = item.Gender;
ctl.Age = Convert.ToInt32(item.Age);
ctl.Mobile = item.Mobile;
ctl.Workphone = item.WorkPhone;
ctl.Designation = item.Designation;
ctl.Importancy = item.Importancy;
list.Add(ctl);
}
}
//AND SO ON I HAVE TO CHECK THE OPTIONAL PARAMETERS......
//else if()
//{
//}
}
And In below code If I try to use switch statement to bind query based condition its throwing error:
Code 2:Switch statement:
public static void LoadGrid(ref GridView gvMain, string cID, string desig = "All", string importancy = "All", string status = "All")
{
int _cId = Convert.ToInt32(cID);
List<clsclass> list = new List<clsclass>();
var db = new MyEntities();
var query;
switch (query)
{
case _cId == 0 && desig == "All" && importancy == "All" && satus == "All":
query = from b in db.ConstituencyLeaders select b;
case _cId != 0 && desig == "All" && importancy == "All" && satus == "All":
query = from b in db.ConstituencyLeaders where b.ConstituencyID == _cId select b;
}
foreach (var item in query)
{
clsclass cl = new clsclass();
cl.LeaderId = item.LID;
//...remaining members add
list.Add(cl);
}
gvMain.DataSource = list;
gvMain.DataBind();
}
So basically I got two questions How to shorten the codes to capture the optional parameters if switch statement is better option then how would I achieve var query from Case:
any help much appreciated.

What you can do is.
var query = db.Members.AsQuerryable();
if(_cid != "")
{
query = query.where(table => table.CID == _cId);
}
Then use that in your statement
var result = from table in query where table.CID == _cId select table;
or we also used to do or statements.
var query= from table in query where (table.CID == _cId || _cId = "") select table;
so if the value is empty it just goes through or if there is a value it checks.