decimal? with Left outer join gets null reference in LINQ - linq

I am trying to do left outer join in LINQ for two vars but on selecting required coloumns, I get Object reference not set to an instance of an object error where I want Nullable decimal.
var FLS = (from ee in SumTillFYEnd
join es in SumTillFYStart on ee.Account equals es.Account into temp
from t in temp.DefaultIfEmpty()
select new
{
Account = ee.Account, // As of here it works
BeginDr = (t.DrStartCF == 0) ? (decimal?) null : t.DrStartCF // Here I get error Object reference not set to an instance of an object.
});
Some times SumTillFYEnd and some times SumTillFYStart becomes null. I want to join should work with default values, in case any one or both is null.

The problem is attempting to cast null to decimal?. You cannot ever directly cast null to another type, nullable or not. That will always cause a NullReferenceException. What you want instead is default. In other words, replace:
(decimal?)null
With
default(decimal?)

I solved this using a default class.
The reason I am seeing is that decimal can not be null so it either needs to set for a default value either 0 or decimal.MinValue
So, you require to have default class for SumTillFYStart like
var defaultSumTillFYStart = new SumTillFYStart { Account = string.Empty, DrStartCF =0};
With above in context, then in your piece of code replace
from t in temp.DefaultIfEmpty()
with this
from t in temp.DefaultIfEmpty(defaultSumTillFYStart)
I have a linqPad working written below but for different subset; I think it will help somebody:
void Main()
{
List<Debtor> debtors = new List<Debtor>();
List<SecurityHolding> holdings = new List<SecurityHolding>();
//Initialize Debtor
debtors.Add(new Debtor(){
AccountId = "J1",
OutstandingValue = 501.95M
});
debtors.Add(new Debtor(){
AccountId = "J2",
OutstandingValue = 75.68M
});
debtors.Add(new Debtor(){
AccountId = "J3",
OutstandingValue = 100.01M
});
//Initialize Security Holding
holdings.Add(new SecurityHolding(){
AccountId = "J2",
SecurityHoldingValue = 100M
});
holdings.Add(new SecurityHolding(){
AccountId = "J3",
SecurityHoldingValue = 200M
});
var defaultHolding = new SecurityHolding { AccountId= string.Empty, SecurityHoldingValue = 0};
var result = (from d in debtors
join p in holdings
on d.AccountId equals p.AccountId into temp
from t in temp.DefaultIfEmpty(defaultHolding)
select new
{
AccountId = d.AccountId,
OutstandingValue = d.OutstandingValue,
HoldingValue = (decimal?)t.SecurityHoldingValue
});
result.Dump();
}
// Define other methods and classes here
public class Debtor
{
public string AccountId {get;set;}
public decimal OutstandingValue {get;set;}
}
public class SecurityHolding
{
public string AccountId {get;set;}
public decimal SecurityHoldingValue {get;set;}
}
Here the output:

Related

How to call Expression Func with two input parameters

I have following Expression Func which is receiving two input paramters, first is Person Object, second is bool and returning another type of Object PersonProfile
private Exression<Func<Person, bool, PersonProfile>> PersonProfileProjection => (person, isValid) =>
new PersonProfile
{
FirstName = person.FirstName,
HasAddress = isValid ? person.Address1 : null
};
And I am trying to call this while fetching Person table from dbContext.
_dbContext.Persons.Select(PersonProfileProjection);
I am confused how to send boolean parameter inside PersonProfileProjection. It works when I only put one input and one output parameter like this. But I want extra boolean input as well.
Any help would be highly appreciated.
You can follow Microsoft documentation for this : Expression Class
One sample created for SQLite that show above function usage.
public void GetData()
{
var connection = new SQLiteConnection(#"Data Source=database.sqlite;Version=3;");
var context = new DataContext(connection);
connection.Open();
var createtableQuery = #"
drop table Company;
CREATE TABLE[Company]
(
[ID] INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
[Seats] INTEGER NOT NULL
);
";
var command = new SQLiteCommand(createtableQuery, connection);
command.ExecuteNonQuery();
Company com = new Company()
{
Id = 6,
Seats = 7
};
context.GetTable<Company>().InsertOnSubmit(com);
context.SubmitChanges();
var companies = context.GetTable<Company>();
foreach (var company in companies)
{
Console.WriteLine("Company: {0} {1}",
company.Id, company.Seats);
}
//compile Expression using Compile method to invoke it as Delegate
Func<int,int, Company> PersonProfileProjectionComp = PersonProfileProjection.Compile();
var dd = companies.Select(p => PersonProfileProjectionComp(p.Id,p.Seats));
//// Below line inline use. Both works.
//var dd = companies.Select(p => PersonProfileProjection.Compile().Invoke(p.Id,p.Seats));
}
private System.Linq.Expressions.Expression<Func<int, int, Company>> PersonProfileProjection => (person, seats) =>
new Company
{
Id = person,
Seats = seats
};
or in one line use this :
PersonProfileProjection.Compile().Invoke(person, isValid)
You could declare it as a Func instead of an expression:
private Func<Person, bool, PersonProfile> PersonProfileProjection => (person, isValid) =>
new PersonProfile
{
FirstName = person.FirstName,
HasAddress = isValid // do what you meant to do
};
... and call it as:
_dbContext.Persons.Select(p => PersonProfileProjection(p, true));
You could as well write an ordinary method:
private PersonProfile PersonProfileProjection(Person person, bool isValid)
{
return new PersonProfile
{
FirstName = person.FirstName,
HasAddress = isValid // do what you want to do
};
}
...and call it the same way:
_dbContext.Persons.Select(p => PersonProfileProjection(p, true));

EF Core LINQ use scalar function

I use Entity Framework Core 2.1.
I have a scalar function in the database which adds specified number of days.
I created an extension method to execute it:
public static class AdventureWorks2012ContextExt
{
public static DateTime? ExecFn_AddDayPeriod(this AdventureWorks2012Context db, DateTime dateTime, int days, string periodName)
{
var sql = $"set #result = dbo.[fn_AddDayPeriod]('{dateTime.ToString("yyyy-MM-dd HH:mm:ss.fff")}', {days}, '{periodName}')";
var output = new SqlParameter { ParameterName = #"result", DbType = DbType.DateTime, Size = 16, Direction = ParameterDirection.Output };
var result = db.Database.ExecuteSqlCommand(sql, output);
return output.Value as DateTime?;
}
}
I try to use a scalar function in the query (to simplify things I use AdventureWorks2012) as follows:
var persons =
(from p in db.Person
join pa in db.Address on p.BusinessEntityId equals pa.AddressId
where p.ModifiedDate > db.ExecFn_AddDayPeriod(pa.ModifiedDate, 100, "DayPeriod_day")
select p).ToList();
But get an System.InvalidOperationException: 'A second operation started on this context before a previous operation completed. Any instance members are not guaranteed to be thread safe.'
How can I achieve this?
UPDATE:
I managed to do it with the help of Ivan's answer:
var persons =
(from p in db.Person
join bea in db.BusinessEntityAddress on p.BusinessEntityId equals bea.BusinessEntityId
join a in db.Address on bea.AddressId equals a.AddressId
where p.ModifiedDate > AdventureWorks2012ContextFunctions.AddDayPeriod(a.ModifiedDate, 100, "DayPeriod_day")
select p).ToList();
But now I need to update ModifiedDate for filtered persons. So I'm doing like this:
var persons =
(from p in db.Person
join bea in db.BusinessEntityAddress on p.BusinessEntityId equals bea.BusinessEntityId
join a in db.Address on bea.AddressId equals a.AddressId
let date = AdventureWorks2012ContextFunctions.AddDayPeriod(a.ModifiedDate, 100, "DayPeriod_day")
where p.ModifiedDate > date
select new { Person = p, NewDate = date }).ToList();
foreach (var p in persons)
p.Person.ModifiedDate = p.NewDate ?? DateTime.Now;
db.SaveChanges();
But got System.NotSupportedException: 'Specified method is not supported.'
How can I use scalar function in select statement?
I tried to split the query by two parts:
var filteredPersons = // ok
(from p in db.Person
join bea in db.BusinessEntityAddress on p.BusinessEntityId equals bea.BusinessEntityId
join a in db.Address on bea.AddressId equals a.AddressId
where p.ModifiedDate > AdventureWorks2012ContextFunctions.AddDayPeriod(a.ModifiedDate, 100, "DayPeriod_day")
select new { Person = p, a.ModifiedDate }).ToList();
var persons = // here an exception occurs
(from p in filteredPersons
select new { Person = p, NewDate = AdventureWorks2012ContextFunctions.AddDayPeriod(p.ModifiedDate, 100, "DayPeriod_day") }).ToList();
Instead of invoking the function client side (which is this particular case happens as part of the client evaluation of the query filter, while the query reading is still in progress), you can use EF Core Database scalar function mapping so it
can be used in LINQ queries and translated to SQL.
One way to do that is to create a public static method in the derived context class and mark it with DbFunction attribute:
public partial class AdventureWorks2012Context
{
[DbFunction("fn_AddDayPeriod")]
public static DateTime? AddDayPeriod(DateTime dateTime, int days, string periodName) => throw new NotSupportedException();
}
and use
where p.ModifiedDate > AdventureWorks2012Context.AddDayPeriod(pa.ModifiedDate, 100, "DayPeriod_day")
Another way is to create a public static method in another class
public static class AdventureWorks2012DbFunctions
{
[DbFunction("fn_AddDayPeriod")]
public static DateTime? AddDayPeriod(DateTime dateTime, int days, string periodName) => throw new NotSupportedException();
}
but then you'll need to register it with fluent API (which happens automatically for methods defined inside the context derived class):
modelBuilder
.HasDbFunction(() => AdventureWorks2012DbFunctions.AddDayPeriod(default(DateTime), default(int), default(string)));
The usage is the same:
where p.ModifiedDate > AdventureWorksDbFunctions.AddDayPeriod(pa.ModifiedDate, 100, "DayPeriod_day")

Entity Framework cycle of data

I have an Account object, which has many Transactions related to it.
In one method, I get all transactions for a particular account.
var transactionlines = (from p in Context.account_transaction
.Include("account_transaction_line")
// .Include("Account")
.Include("account.z_account_type")
.Include("account.institution")
.Include("third_party")
.Include("third_party.z_third_party_type")
.Include("z_account_transaction_type")
.Include("account_transaction_line.transaction_sub_category")
.Include("account_transaction_line.transaction_sub_category.transaction_category")
.Include("z_account_transaction_entry_type")
.Include("account_transaction_line.cost_centre")
where p.account_id == accountId
&& p.deleted == null
select p).ToList();
This is meant to return me a list of transactions, with their related objects. I then pass each object to a Translator, which translates them into data transfer objects, which are then passed back to my main application.
public TransactionDto TranslateTransaction(account_transaction source)
{
LogUserActivity("in TranslateTransaction");
var result = new TransactionDto
{
Id = source.id,
Version = source.version,
AccountId = source.account_id,
// Account = TranslateAccount(source.account, false),
ThirdPartyId = source.third_party_id,
ThirdParty = TranslateThirdParty(source.third_party),
Amount = source.transaction_amount,
EntryTypeId = source.account_transaction_entry_type_id,
EntryType = new ReferenceItemDto
{
Id = source.account_transaction_entry_type_id,
Description = source.z_account_transaction_entry_type.description,
Deleted = source.z_account_transaction_entry_type.deleted != null
},
Notes = source.notes,
TransactionDate = source.transaction_date,
TransactionTypeId = source.account_transaction_type_id,
TransactionType = new ReferenceItemDto
{
Id = source.z_account_transaction_type.id,
Description = source.z_account_transaction_type.description,
Deleted = source.z_account_transaction_type.deleted != null
}
};
... return my object
}
The problem is:
An account has Transactions, and a Transaction therefore belongs to an Account. It seems my translators are being called way too much, and reloading a lot of data because of this.
When I load my transaction object, it's 'account' property has a'transactions' propery, which has a list of all the transactions associated to that account. Each transaction then has an account property... and those account peroprties again, have a list of all the transactions... and on and on it goes.
Is there a way I can limit the loading to one level or something?
I have this set:
Context.Configuration.LazyLoadingEnabled = false;
I was hoping my 'Includes' would be all that is loaded... Don't load 'un-included' related data?
As requested, here is my TranslateAccount method:
public AccountDto TranslateAccount(account p, bool includeCardsInterestRateDataAndBalance)
{
LogUserActivity("in TranslateAccount");
if (p == null)
return null;
var result =
new AccountDto
{
Id = p.id,
Description = p.description,
PortfolioId = p.institution.account_portfolio_id,
AccountNumber = p.account_number,
Institution = TranslateInstitution(p.institution),
AccountType = new ReferenceItemDto
{
Id = p.account_type_id,
Description = p.z_account_type.description
},
AccountTypeId = p.account_type_id,
InstitutionId = p.institution_id,
MinimumBalance = p.min_balance,
OpeningBalance = p.opening_balance,
OpeningDate = p.opening_date
};
if (includeCardsInterestRateDataAndBalance)
{
// Add the assigned cards collection
foreach (var card in p.account_card)
{
result.Cards.Add(new AccountCardDto
{
Id = card.id,
AccountId = card.account_id,
Active = card.active,
CardHolderName = card.card_holder_name,
CardNumber = card.card_number,
ExpiryDate = card.expiry
});
}
// Populate the current interest rate
result.CurrentRate = GetCurrentInterestRate(result.Id);
// Add all rates to the account
foreach (var rate in p.account_rate)
{
result.Rates.Add(
new AccountRateDto
{
Id = rate.id,
Description = rate.description,
Deleted = rate.deleted != null,
AccountId = rate.account_id,
EndDate = rate.end_date,
Rate = rate.rate,
StartDate = rate.start_date
});
}
result.CurrentBalance = CurrentBalance(result.Id);
}
LogUserActivity("out TranslateAccount");
return result;
}
The entity framework context maintains a cache of data that has been pulled out of the database. Regardless of lazy loading being enabled/disabled, you can call Transaction.Account.Transactions[0].Account.Transactions[0]... as much as you want without loading anything else from the database.
The problem is not in the cyclical nature of entity framework objects - it is somewhere in the logic of your translation objects.

EF single entity problem

I need to return a single instance of my viewmodel class from my repository in order to feed this into a strongly-typed view
In my repository, this works fine for a collection of viewmodel instances:
IEnumerable<PAWeb.Domain.Entities.Section> ISectionsRepository.GetSectionsByArea(int AreaId)
{
var _sections = from s in DataContext.Sections where s.AreaId == AreaId orderby s.Ordinal ascending select s;
return _sections.Select(x => new PAWeb.Domain.Entities.Section()
{
SectionId = x.SectionId,
Title = x.Title,
UrlTitle = x.UrlTitle,
NavTitle = x.NavTitle,
AreaId = x.AreaId,
Ordinal = x.Ordinal
}
);
}
But when I attempt to obtain a single entity, like this:
public PAWeb.Domain.Entities.Section GetSection(int SectionId)
{
var _section = from s in DataContext.Sections where s.SectionId == SectionId select s;
return _section.Select(x => new PAWeb.Domain.Entities.Section()
{
SectionId = x.SectionId,
Title = x.Title,
UrlTitle = x.UrlTitle,
NavTitle = x.NavTitle,
AreaId = x.AreaId,
Ordinal = x.Ordinal
}
);
}
I get
Error 1 Cannot implicitly convert type
'System.Linq.IQueryable<PAWeb.Domain.Entities.Section>' to
'PAWeb.Domain.Entities.Section'. An explicit conversion exists
(are you missing a cast?)"
This has got to be simple, but I'm new to c#, and I can't figure out the casting. I tried (PAWeb.Domain.Entities.Section) in various places, but no success. Can anyone help??
Your query is returning an IQueryable, which could have several items. For example, think of the difference between an Array or List of objects and a single object. It doesn't know how to convert the List to a single object, which one should it take? The first? The last?
You need to tell it specifically to only take one item.
e.g.
public PAWeb.Domain.Entities.Section GetSection(int SectionId)
{
var _section = from s in DataContext.Sections where s.SectionId == SectionId select s;
return _section.Select(x => new PAWeb.Domain.Entities.Section()
{
SectionId = x.SectionId,
Title = x.Title,
UrlTitle = x.UrlTitle,
NavTitle = x.NavTitle,
AreaId = x.AreaId,
Ordinal = x.Ordinal
}
).FirstOrDefault();
}
This will either return the first item, or null if there are no items that match your query. In your case that won't happen unless the table is empty since you don't have a where clause.

Need Help Translating SQL Server UNION Syntax to LINQ

I have the below SQL which works just fine:
SELECT Message, CreateDate, AccountId, AlertTypeId
FROM dbo.Alerts
UNION
SELECT TOP (100) PERCENT Status, CreateDate, AccountId,
(SELECT 10 AS Expr1) AS AlertTypeId
FROM dbo.StatusUpdates
WHERE AccountId = PassedInParameter
ORDER BY CreateDate DESC
I am trying to convert it to LINQ, which doesn't work just fine :) Obviously, there is a lot wrong here - it is just a rough start. It does not account for the above temp column or the order by condition and the generics / return type ambiguity is my attempt to make sense of the two different return types:
public List<T> GetSomething<T>(Int32 accountId)
{
List<T> result;
using (DataContext dc = _conn.GetContext())
{
IEnumerable<Alert> alerts = (from a in dc.Alerts
where a.AccountId == accountId
select a);
IEnumerable<StatusUpdate> updates = (from s in dc.StatusUpdates
where s.AccountId == accountId
select s);
IEnumerable<T> obj = alerts.Union(updates);
result = obj.ToList();
}
return result;
}
The problems I am having are:
1) I am dealing with two different types (Alerts and StatusUpdate) in my selects and
I am not sure how to combine them (or what type to return). I am guessing this might
be solved with generics?
2) In my SQL, I have this code: (SELECT 10 AS Expr1) AS AlertTypeId which adds the value ten to the temp column AlertTypeId (allowing the union to match it to Alert's real column AlertTypeId). How are temp columns such as this accomplished in LINQ / how do I do this?
Thanks for your help.
EDIT---------------------------------EDIT------------------------------------------EDIT
OK, I am a little further along. Below is what I have currently. You will notice I added some logic to return the updates for friend relations. I also made this a generic method of type IList given that alerts and updates have to be generic to agree. I pass in StatusUpdate in the calling method (further down below).
public IList GetUpdatesByAccountId<T>(Int32 accountId)
{
List<Friend> friends = _friendRepository.GetFriendsByAccountId(accountId);
using (DataContext dc = _conn.GetContext())
{
// Get all the account ids related to this user
var friendAccountIds =
friends.Select(friend => friend.MyFriendsAccountId).Distinct();
friendAccountIds = friendAccountIds.Concat(new[] { accountId });
var updates =
dc.StatusUpdates.Where(s => s.AccountId.HasValue && friendAccountIds.Contains(s.AccountId.Value)).Select(
s => new { Alert = (Alert)null, StatusUpdate = s});
var alerts =
dc.Alerts.Where(a => a.AccountId == accountId).Select(
a => new {Alert = a, StatusUpdate = (StatusUpdate) null});
var obj = updates.Union(alerts).Take(100);
return obj.OrderByDescending(su => su.StatusUpdate.CreateDate).ToList();
}
}
And, the calling method:
protected void LoadStatus()
{
repStatusUpdates.DataSource = _statusRepository
.GetUpdatesByAccountId<StatusUpdate>(_userSession.CurrentUser.AccountId);
repStatusUpdates.DataBind();
}
AND here are the interfaces to the repositories I am using to access my Alert and StatusUpdate tables via LINQ:
public interface IAlertRepository
{
List<Alert> GetAlertsByAccountId(Int32 accountId);
void SaveAlert(Alert alert);
void DeleteAlert(Alert alert);
}
public interface IStatusUpdateRepository
{
StatusUpdate GetStatusUpdateById(Int32 statusUpdateId);
List<StatusUpdate> GetStatusUpdatesByAccountId(Int32 accountId);
List<StatusUpdate> GetFriendStatusUpdatesByAccountId(Int32 accountId, Boolean addPassedInAccount);
void SaveStatusUpdate(StatusUpdate statusUpdate);
List<StatusUpdate> GetTopNStatusUpdatesByAccountId(Int32 accountId, Int32 number);
List<StatusUpdate> GetTopNFriendStatusUpdatesByAccountId(Int32 accountId, Int32 number, Boolean addPassedInAccount);
}
Current Problems:
1) When I compile this code, I get this strange error:
Unable to cast object of type
'System.Data.Linq.SqlClient.SqlNew' to
type
'System.Data.Linq.SqlClient.SqlValue'.
The only reading I can find on it is this link although there isn't a clear solution there (at least that I can tell). However, if the above LINQ code does not look good to you, maybe whatever you suggest will cause this error to disappear.
2) The above code is still not accounting for this line from the original SQL:
(SELECT 10 AS Expr1) AS AlertTypeId
but this is minor.
Thanks again for the help.
Try this (i converted the StatusUpdate to an alert, if this isn't acceptable, you're going to have to either convert the Alert to a StatusUpdate, or create a new class):
var alerts = (from a in dc.Alerts
where a.AccountId == accountId
select a);
var updates = (from s in dc.StatusUpdates
where s.AccountId == accountId
select s)
.OrderByDescending( x => x.CreateDate)
.Take(100)
.Select( x => new Alert
{
Message = x.Percent.ToString(),
CreateDate = x.CreateDate,
AccountId = x.AccountId,
AlertTypeId = 10 // Is this right?
}
);
var obj = alerts.Union(updates);
result = obj.ToList();
The reason I do the Select last is so that you don't have to construct a new alert for all the results your are not using.
This will give you a list of Alerts.
Using a generic in this situation is sort of hard to pull off. For instance, you can't do this:
IQueryable alerts = (from a in _alerts
where a.AccountId == accountId
select a);
Because that implicitly converts a to type T. Even if you try to limit what T implements or inherits from:
public List<T> GetSomething<T>(Int32 accountId) where T : IAlert// Interface that both StatusUpdates and IAlert implement
public List<T> GetSomething<T>(Int32 accountId) where T : Alert
public List<T> GetSomething<T>(Int32 accountId) where T : AlertBase // Base class for both Status and Alert
You'll still run into problems because there is no way to statically know exactly what type T is, so you cannot know if it can be converted from Alert and StatusUpdate.
An alternative is to explicitly use IAlert as your return type:
public List<IAlert> GetSomething(Int32 accountId)
With IAlert:
public interface IAlert
{
int AccountId { get; set; }
int AlertTypeId { get; set; }
DateTime CreateDate { get; set; }
string Message { get; set; }
}
If you have have both Alert and StatusUpdate implement IAlert, you could rewrite it as so:
IQueryable<IAlert> alerts = (from a in dc.Alerts
where a.AccountId == accountId
select a);
IQueryable<IAlert> updates = (from s in dc.StatusUpdates
where s.AccountId == accountId
select s)
.OrderByDescending( x => x.CreateDate)
.Take(100);
var obj = alerts.Union(updates);
result = obj.ToList();
This is the route I would take instead of passing in some unknown type and trying to limit what it implements or inherits, because casting to that type might still be invalid.
You can only take unions of sequences of equal types. You need to convert alerts and updates to sequences of a common type, then take the union. You can do so using anonymous types. Especially useful if the types don't have anything in common.
//this is a hack and probably not what you would want to use.
var alerts =
from a in dc.Alerts
where a.AccountId == accountId
select new { Alert = a, StatusUpdate = (StatusUpdate)null };
var updates =
from s in dc.StatusUpdates
where s.AccountId == accountId
select new { Alert = (Alert)null, StatusUpdate = s };
//both are sequences of anonymous type with properties:
// Alert (of type Alert)
// StatusUpdate (of type StatusUpdate)
var obj = alerts.Union(updates);
If you have fields in common, you'd still use anonymous types except you'd include the known fields.
var alerts =
from a in dc.Alerts
where a.AccountId == accountId
select new
{
a.Message, //assuming is a string
Status = (string)null,
a.CreateDate,
a.AccountId,
a.AlertTypeId //assuming is an int
};
var updates =
(from s in dc.StatusUpdates
where s.AccountId == accountId
select new
{
Message = (string)null,
s.Status, //assuming is a string
s.CreateDate,
s.AccountId,
AlertTypeId = 10 //this should handle the "10 AS AlertTypeId" part
}).OrderByDescending(s => s.CreateDate);
var obj = alerts.Union(updates);
The key is that both anonymous types has the same exact properties of the same exact types. Then you can take the union between them both.

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