Develop Reference

How do I convert SQL Query to Lambda?

I have the following SQL query that returns the results I need:
SELECT
STAFF_ID
FROM [dbo].[StaffTable]
WHERE STAFF_ID NOT IN (SELECT STAFF_ID
FROM [dbo].[StaffingTable]
WHERE [DATE] = #DATE
AND MODEL_ID = #Model)
I have the following controller method to try and return the correct results:
public JsonResult GetStaffResults(DateTime date, string modelId)
{
Guid modelGuid = Guid.Parse(modelId);
var settings = new JsonSerializerSettings();
var staff = context.StaffTable.Select(c => new
{
Id = c.StaffId,
Name = c.StaffName
});
var staffing = context.StaffingTable.Select(c => new
{
modelId = c.ModelId,
manufacturerId = c.ManufacturerId,
staffId = c.StaffId,
date = c.Date,
recordId = c.RecordId
});
var staffResults = staff.Where(p => staffing.Select(o => o.modelId).First() == modelGuid && !staffing.Select(o => o.date).Contains(date));
return Json(shiftResults, settings);
}
However, I'm struggling with the Lambda expression, it returns no results so I've missed something somewhere.

You can try something like this:
public JsonResult GetStaffResults(DateTime date, string modelId)
{
Guid modelGuid = Guid.Parse(modelId);
var settings = new JsonSerializerSettings();
var staffQuery = context.StaffTable
.Where(s => !context
.StaffingTable
.Any(st => st.StaffId = s.StaffId && st.modelId == modelGuid && st.date == date))
.Select(c => new
{
Id = c.StaffId,
Name = c.StaffName
});
return Json(staffQuery.ToList(), settings);
}

You are doing separate query with Select which has a performance issue as the queries will return IEnumerable<T> objects. If you want to have separate queries then try to get the query results as IQueryable<T> which will construct the queries and will load data at the end.
For example:
var query =
from st in context.StaffTable
where !(from stff in context.StaffingTable
select stff.CustomerID)
where stff.MODEL_ID = ModelIdVariable AND stff.DATE = DATEVariable
.Contains(st.CustomerID)
select st;
Declare and populate the ModelIdVariable and DATEVariable variables before the query.
Then you can do query.ToList<T>() where you need the data to be loaded.

How do you reuse mapping functions on Nested entities in Entity Framework?

I have seen multiple questions that are similar to this one but I think my case is slightly different. I'm using EF6 to query the database and I'm using data projection for better queries.
Given that performance is very important on this project I have to make sure to just read the actual fields that I will use so I have very similar queries that are different for just a few fields as I have done this I have noticed repetition of the code so I'm been thinking on how to reuse code this is currently what I Have:
public static IEnumerable<FundWithReturns> GetSimpleFunds(this DbSet<Fund> funds, IEnumerable<int> fundsId)
{
IQueryable<Fund> query = GetFundsQuery(funds, fundsId);
var results = query
.Select(f => new FundWithReturns
{
Category = f.Category,
ExpenseRatio = f.ExpenseRatio,
FundId = f.FundId,
Name = f.Name,
LatestPrice = f.LatestPrice,
DailyReturns = f.FundDailyReturns
.Where(dr => dr.AdjustedValue != null)
.OrderByDescending(dr => dr.CloseDate)
.Select(dr => new DailyReturnPrice
{
CloseDate = dr.CloseDate,
Value = dr.AdjustedValue.Value,
}),
Returns = f.Returns.Select(r => new ReturnValues
{
Daily = r.AdjDaily,
FiveYear = r.AdjFiveYear,
MTD = r.AdjMTD,
OneYear = r.AdjOneYear,
QTD = r.AdjQTD,
SixMonth = r.AdjSixMonth,
ThreeYear = r.AdjThreeYear,
YTD = r.AdjYTD
}).FirstOrDefault()
})
.ToList();
foreach (var result in results)
{
result.DailyReturns = result.DailyReturns.ConvertClosingPricesToDailyReturns();
}
return results;
}
public static IEnumerable<FundListVm> GetFundListVm(this DbSet<Fund> funds, string type)
{
return funds
.Where(f => f.StatusCode == MetisDataObjectStatusCodes.ACTIVE
&& f.Type == type)
.Select(f => new FundListVm
{
Category = f.Category,
Name = f.Name,
Symbol = f.Symbol,
Yield = f.Yield,
ExpenseRatio = f.ExpenseRatio,
LatestDate = f.LatestDate,
Returns = f.Returns.Select(r => new ReturnValues
{
Daily = r.AdjDaily,
FiveYear = r.AdjFiveYear,
MTD = r.AdjMTD,
OneYear = r.AdjOneYear,
QTD = r.AdjQTD,
SixMonth = r.AdjSixMonth,
ThreeYear = r.AdjThreeYear,
YTD = r.AdjYTD
}).FirstOrDefault()
}).OrderBy(f=>f.Symbol).Take(30).ToList();
}
I'm trying to reuse the part where I map the f.Returns so I tried created a Func<> like the following:
private static Func<Return, ReturnValues> MapToReturnValues = r => new ReturnValues
{
Daily = r.AdjDaily,
FiveYear = r.AdjFiveYear,
MTD = r.AdjMTD,
OneYear = r.AdjOneYear,
QTD = r.AdjQTD,
SixMonth = r.AdjSixMonth,
ThreeYear = r.AdjThreeYear,
YTD = r.AdjYTD
};
and then use like this:
public static IEnumerable<FundListVm> GetFundListVm(this DbSet<Fund> funds, string type)
{
return funds
.Where(f => f.StatusCode == MetisDataObjectStatusCodes.ACTIVE
&& f.Type == type)
.Select(f => new FundListVm
{
Category = f.Category,
Name = f.Name,
Symbol = f.Symbol,
Yield = f.Yield,
ExpenseRatio = f.ExpenseRatio,
LatestDate = f.LatestDate,
Returns = f.Returns.Select(MapToReturnValues).FirstOrDefault()
}).OrderBy(f=>f.Symbol).Take(30).ToList();
}
The compiler is ok with it but at runtime, it crashes and says: Internal .NET Framework Data Provider error 1025
I tried to convert the Func into Expression like I read on some questions and then using compile() but It didn't work using AsEnumerable is also not an option because It will query all the fields first which is what I want to avoid.
Am I trying something not possible?
Thank you for your time.

It definitely needs to be Expression<Func<...>>. But instead of using Compile() method (not supported), you can resolve the compile time error using the AsQueryable() method which is perfectly supported (in EF6, the trick doesn't work in current EF Core).
Given the modified definition
private static Expression<Func<Return, ReturnValues>> MapToReturnValues =
r => new ReturnValues { ... };
the sample usage would be
Returns = f.Returns.AsQueryable().Select(MapToReturnValues).FirstOrDefault()

How to sort in LINQ If Join other database

Sort in LINQ
I have 2 database CustomerEntities and BillEntities
I want to get CustomerName from CustomerEntities and sort it but it have no data and I want .ToList() just once time because it slow if used many .ToList()
using (var db1 = new CustomerEntities())
{ using (var db2 = new BillEntities())
{
var CustomerData = db1.Customer.Select(s=> new{s.CustomerCode,s.CustomerName}).ToList();
var BillData = (from t1 in db2.Bill
select new {
BillCode = t1.Billcode,
CustomerCode = t1.Customer,
CustomerName = ""; //have no data
});
}
if(sorting.status==true)
{
BillData= BillData.OrderBy(o=>o.CustomerName); //can't sort because CustomerName have no data
}
var data = BillData .Skip(sorting.start).Take(sorting.length).ToList(); // I want .ToList() just once time because it slow if used many .ToList()
foreach (var b in data)
{
var Customer = CustomerData.FirstOrDefault(f => f.CustomerCode==b.CustomerCode );
if(CustomerName>!=null)
{
r.CustomerName = Customer.CustomerName; //loop add data CustomerName
}
}
}
I have no idea to do it. Help me please

I'm not sure if I understand your code but what about this:
var BillData = (from t1 in db2.Bill
select new {
BillCode = t1.Billcode,
CustomerCode = t1.Customer,
CustomerName = db1.Customer.FirstOrDefault(c => c.CustormerCode == t1.Customer)?.CustomerName
});
Then you have objects in BillData that holds the CustomerName and you can order by that:
BillData.OrderBy(bd => bd.CustomerName);

If you just want to get CustomerName from your customer Db and sort it, this is what i would have used. I used orderByDescending but you can use OrderBy aswell.
public List<Customer> getLogsByCustomerName(string customername)
{
using (var dbentites = new CustomerEntities())
{
var result = (from res in dbentites.Customer.OrderByDescending(_ => _.CustomerName)
where res.CustomerName == customername
select res).ToList();
return result.ToList();
}
}

StringBuilder within IEnumerable

I have a ControlMeasure table that holds information on each control measure and a ControlMeasurepeopleExposed Table that holds a record for each person exposed in the control measure this could be 1 record or many records.
I Have a controller that populates a List view
For each item in the list, Control Measure, I would like to create a string that shows all the People at risk
e.g.
PeopleString = "Employees, Public, Others";
Ive added a foreach in the controller to show what I'm trying to do however I'm aware that this wont work.
The controller is this:
public ActionResult ControlMeasureList(int raId)
{
//Populate the list
var hazards = new List<Hazard>(db.Hazards);
var controlMeasures = new List<ControlMeasure>(db.ControlMeasures).Where(x => x.RiskAssessmentId == raId);
var cmcombined = (
from g in hazards
join f in controlMeasures
on new { g.HazardId } equals new { f.HazardId }
select new CMCombined
{
Activity = f.Activity,
ControlMeasureId = f.ControlMeasureId,
ExistingMeasure = f.ExistingMeasure,
HazardName = g.Name,
LikelihoodId = f.LikelihoodId,
Rating = f.Rating,
RiskAssessmentId = f.RiskAssessmentId,
SeverityId = f.SeverityId,
}).OrderBy(x => x.Activity).ToList();
var cmPeopleExp = new List<ControlMeasurePeopleExposed>(db.ControlMeasurePeopleExposeds).Where(x => x.RiskAssessmentId == raId);
var peopleExp = from c in cmPeopleExp
join d in db.PeopleExposeds
on c.PeopleExposedId equals d.PeopleExposedId
orderby d.Name
select new RAPeopleExp
{
RAPeopleExpId = c.PeopleExposedId,
PeopleExpId = c.PeopleExposedId,
PeopleExpName = d.Name,
RiskAssessmentId = c.RiskAssessmentId,
ControlMeasureId = c.ControlMeasureId
};
var model = cmcombined.Select(t => new FullControlMeasureListViewModel
{
ControlMeasureId = t.ControlMeasureId,
HazardName = t.HazardName,
LikelihoodId = t.LikelihoodId,
Rating = t.Rating,
SeverityId = t.SeverityId,
Activity = t.Activity,
ExCM = t.ExistingMeasure,
//This section here is where I'm struggling
var PeopleString = new StringBuilder();
foreach (var p in peopleExp)
{
PeopleString.AppendLine(p.PeopleName);
{
PeopleExposed = PeopleString,
});
return PartialView("_ControlMeasureList", model);
}
I know I cant directly put this code in the controller but it does represent what I want to do.

You can't foreach within an object initializer (which is what you're trying to do when instantiating FullControlMeasureListViewModel). You can, however, use a combination of string.Join and peopleExp.Select:
var model = cmcombined.Select(t => new FullControlMeasureListViewModel
{
//other props
PeopleExposed = string.Join(",", peopleExp
.Where(p => p.ControlMeasureId == t.ControlMeasureId)
.Select(p => p.PeopleExpName));
//other props
});

Refactoring C# code - doing more within Linq

The code below is what I currently have and works fine. I feel that I could do more of the work I am doing in Linq instead of C# code.
Is there is anyone out there who can accomplish the same result with more Linq code and less C# code.
public List<Model.Question> GetSurveyQuestions(string type, int typeID)
{
using (eMTADataContext db = DataContextFactory.CreateContext())
{
List<Model.Question> questions = new List<Model.Question>();
List<Linq.Survey_Question> survey_questions;
List<Linq.Survey> surveys = db.Surveys
.Where(s => s.Type.Equals(type) && s.Type_ID.Equals(typeID))
.ToList();
if (surveys.Count > 0)
{
survey_questions = db.Survey_Questions
.Where(sq => sq.Survey_ID == surveys[0].ID).ToList();
foreach (Linq.Survey_Question sq in survey_questions)
{
Model.Question q = Mapper.ToBusinessObject(sq.Question);
q.Status = sq.Status;
questions.Add(q);
}
}
else
{
questions = null;
}
return questions;
}
}
Here is my Mapper function from my Entity to Biz Object
internal static Model.Question ToBusinessObject(Linq.Question q)
{
return new Model.Question
{
ID = q.ID,
Name = q.Name,
Text = q.Text,
Choices = ToBusinessObject(q.Question_Choices.ToList())
};
}
I want my mapper funciton to map the Question Status like so.
internal static Model.Question ToBusinessObject(Linq.Question q)
{
return new Model.Question
{
ID = q.ID,
Name = q.Name,
Text = q.Text,
Choices = ToBusinessObject(q.Question_Choices.ToList()),
Status = q.Survey_Questions[?].Status
};
}
? the issue is this function does not know which survey to pull the status from.
Instead of creating the biz object then setting the Status property in a foreach loop like so
foreach (Linq.Survey_Question sq in survey_questions)
{
Model.Question q = Mapper.ToBusinessObject(sq.Question);
q.Status = sq.Status;
questions.Add(q);
}
I would like to somehow filter the EntitySet<Survey_Question> in the q object above in the calling method, such that there would only be one item in the q.Survey_Questions[?] collection.
below is my database schema and business object schema

What I needed to do was setup a join.
public List<Model.Question> GetSurveyQuestions(string type, int typeID)
{
using (eMTADataContext db = DataContextFactory.CreateContext())
{
return db.Survey_Questions
.Where(s => s.Survey.Type.Equals(type) && s.Survey.Type_ID.Equals(typeID))
.Join(db.Questions,
sq => sq.Question_ID,
q => q.ID,
(sq, q) => Mapper.ToBusinessObject(q, sq.Status)).ToList();
}
}
And then overload my Mapper Function
internal static Model.Question ToBusinessObject(Linq.Question q, string status)
{
return new Model.Question
{
ID = q.ID,
Name = q.Name,
Text = q.Text,
Status = status,
Choices = ToBusinessObject(q.Question_Choices.ToList()),
};
}

from question in db.Survey_Questions
let surveys = (from s in db.Surveys
where string.Equals(s.Type, type, StringComparison.InvariantCultureIgnoreCase) &&
s.Type_ID == typeID)
where surveys.Any() &&
surveys.Contains(s => s.ID == question.ID)
select new Mapper.Question
{
ID = question.Id,
Name = question.Name,
Text = question.Text,
Choices = ToBusinessObject(question.Question_Choices.ToList()),
Status = question.Status
}
Does that get you on the right track?

Why are you duplicating all your classes? You could just extend the LINQ to SQL classes with your business logic - they are partial classes. This is somewhat against the purpose of an OR mapper - persisting business entities.