I've got a complex query written in SQL which works.
SELECT Instruments.Id as [Id], Instruments.ShareCode as [Share Code], Instruments.Name AS [Short Name], Instruments.Description as [Share Name],
InstrumentGames.Instrument_Id,
InstrumentGames.Game_Id, Games.Name AS [Game Name],
Entries.Name AS [Entry Name], AspNetUsers.UserName, AspNetUsers.Id as [User_Id],
Sectors.Name AS Sector_Id, Sectors.ShortName AS Sector
FROM AspNetUsers INNER JOIN
Entries ON AspNetUsers.Id = Entries.User_Id INNER JOIN
Games ON Entries.Game_Id = Games.Id INNER JOIN
InstrumentGames ON Games.Id = InstrumentGames.Game_Id INNER JOIN
Instruments ON InstrumentGames.Instrument_Id = Instruments.Id INNER JOIN
Sectors ON Instruments.Sector_Id = Sectors.Id
WHERE Instruments.Listed = 'true' and InstrumentGames.Game_Id = 2 and Entries.User_Id = 'd28d6552-7d98-476c-82cb-063e7ef45cb6'
I'm using Entity code first models and trying to convert what I have in SQL to a linq query.
I've come up with:
public static Models.Instrument GetShare(string shareSearchCriteria,
Models.Game selectedGame,
string userId)
{
var _db = new JSEChallenge.Models.ApplicationDbContext();
var records = (from instru in _db.Instruments
from e in _db.Entries
where (instru.ShareCode.Contains(shareSearchCriteria) ||
instru.Name.Contains(shareSearchCriteria) ||
instru.Description.Contains(shareSearchCriteria))
where (instru.Listed == true &&
instru.Games.Contains(selectedGame) &&
e.User_Id == userId)
select instru).ToList();
return records.FirstOrDefault();
}
But I keep getting this error:
Unable to create a constant value of type 'X.Models.Game'. Only primitive types or enumeration types are supported in this context.
I think the issue is the m2m table InstrumentGames. In my SQL query I can join it easily but in my C# I cannot. The way I usually find m2m records is syntax like instru.Games.Contains(selectedGame)
Unfortunately I still cannot get this to work.
How do I implement this kind of query in Linq?
Not sure if it will work, but try instru.Games.Any(q => q.Id == selectedGame.Id) instead of instru.Games.Contains(selectedGame).
Hope this helps!
Related
I am able to select data from two tables, But I am getting partial result only while retrieving data from three tables.
var items = from orders in nobleappDbContext.JobOrders.Where(m => m.OrderStat == 0)
join users in nobleappDbContext.users on orders.Uid equals users.Uid
join customers in nobleappDbContext.customers on users.Uid equals customers.Uid into customdata
from m in customdata.DefaultIfEmpty()
select new
{
Eid = orders.Eid,
Uid = orders.Uid,
OrderStat = orders.OrderStat,
Name = m.Name,
Contact = (m.Contact == null) ? 0 : m.Contact
};
return Ok(items);
With this code, I am getting only result (common result) from users table and I am looking for something like UNION or OUTER JOIN.
Any help will be highly appreciated
finally I got exactly what I was looking for, here by posting the answer as I might help someone looking for same. LEFT JOIN with Entity Framework is the key
var query = from a in authurs
join b in books on a.Id equals b.AuthorId into auth_books
from left in auth_books.DefaultIfEmpty()
join bs in booksSeries on left.BookSeriesId equals bs.Id into books_bookseries
from left2 in books_bookseries.DefaultIfEmpty()
select new
{
Author = a.Name,
Book = left.Name,
BookSeries = left2.Description
};
var resList2 = query.ToList();
refer this link for further clarification.
I am comming to ASP .NET Core from PHP w/ MySQL.
The problem:
For the illustration, suppose the following two tables:
T: {ID, Description, FK} and States: {ID, ID_T, Time, State}. There is 1:n relationship between them (ID_T references T.ID).
I need all the records from T with some specific value of FK (lets say 1) along with the related newest record in States (if any).
In terms of SQL it can be written as:
SELECT T.ID, T.Description, COALESCE(s.State, 0) AS 'State' FROM T
LEFT JOIN (
SELECT ID_T, MAX(Time) AS 'Time'
FROM States
GROUP BY ID_T
) AS sub ON T.ID = sub.ID_T
LEFT JOIN States AS s ON T.ID = s.ID_T AND sub.Time = s.Time
WHERE FK = 1
I am struggling to write an efficient equivalent query in LINQ (or the fluent API). The best working solution I've got so far is:
from t in _context.T
where t.FK == 1
join s in _context.States on t.ID equals o.ID_T into _s
from s in _s.DefaultIfEmpty()
let x = new
{
id = t.ID,
time = s == null ? null : (DateTime?)s.Time,
state = s == null ? false : s.State
}
group x by x.id into x
select x.OrderByDescending(g => g.time).First();
When I check the resulting SQL query in the output window when executed it is just like:
SELECT [t].[ID], [t].[Description], [t].[FK], [s].[ID], [s].[ID_T], [s].[Time], [s].[State]
FROM [T] AS [t]
LEFT JOIN [States] AS [s] ON [T].[ID] = [s].[ID_T]
WHERE [t].[FK] = 1
ORDER BY [t].[ID]
Not only it selects more columns than I need (in the real scheme there are more of them). There is no grouping in the query so I suppose it selects everything from the DB (and States is going to be huge) and the grouping/filtering is happening outside the DB.
The questions:
What would you do?
Is there an efficient query in LINQ / Fluent API?
If not, what workarounds can be used?
Raw SQL ruins the concept of abstracting from a specific DB technology and its use is very clunky in current Entity Framework Core (but maybe its the best solution).
To me, this looks like a good example for using a database view - again, not really supported by Entity Framework Core (but maybe its the best solution).
What happens if you try to do a more straight forward translation to LINQ?
var latestState = from s in _context.States
group s by s.ID_T into sg
select new { ID_T = sg.Key, Time = sg.Time.Max() };
var ans = from t in _context.T
where t.FK == 1
join sub in latestState on t.ID equals sub.ID_T into subj
from sub in subj.DefaultIfEmpty()
join s in _context.States on new { t.ID, sub.Time } equals new { s.ID, s.Time } into sj
from s in sj.DefaultIfEmpty()
select new { t.ID, t.Description, State = (s == null ? 0 : s.State) };
Apparently the ?? operator will translate to COALESCE and may handle an empty table properly, so you could replace the select with:
select new { t.ID, t.Description, State = s.State ?? 0 };
OK. Reading this article (almost a year old now), Smit's comment to the original question and other sources, it seems that EF Core is not really production ready yet. It is not able to translate grouping to SQL and therefore it is performed on the client side, which may be (and in my case would be) a serious problem. It corresponds to the observed behavior (the generated SQL query does no grouping and selects everything in all groups). Trying the LINQ queries out in Linqpad it always translates to a single SQL query.
I have downgraded to EF6 following this article. It required some changes in my model's code and some queries. After changing .First() to .FirstOrDefault() in my original LINQ query it works fine and translates to a single SQL query selecting only the needed columns. The generated query is much more complex than it is needed, though.
Using a query from NetMage's answer (after small fixes), it results in a SQL query almost identical to my own original SQL query (there's only a more complex construct than COALESCE).
var latestState = from s in _context.States
group s by s.ID_T into sg
select new { ID = sg.Key, Time = sg.Time.Max() };
var ans = from t in _context.T
where t.FK == 1
join sub in latestState on t.ID equals sub.ID into subj
from sub in subj.DefaultIfEmpty()
join s in _context.States
on new { ID_T = t.ID, sub.Time } equals new { s.ID_T, s.Time }
into sj
from s in sj.DefaultIfEmpty()
select new { t.ID, t.Description, State = (s == null ? false : s.State) };
In LINQ it's not as elegant as my original SQL query but semantically it's the same and it does more or less the same thing on the DB side.
In EF6 it is also much more convenient to use arbitrary raw SQL queries and AFAIK also the database views.
The biggest downside of this approach is that full .NET framework has to be targeted, EF6 is not compatible with .NET Core.
I have two tables:
Phase :
long ID
string Name
and another Activity :
long ID
string Name
long PhaseID
I already know the name of the phases and I want to get the activity for those particular phases. Do i add PhaseName to the activity table or do I do it through join in LINQ?
Maybe something like this?
var query = from a in entities.Activities
join p in entities.Phases on a.PhaseId equals p.Id
where p.Name == "Preplanning"
... and here im not sure how to finish this query..
Thanks for your help!
The code that you've provided will use an Inner Join to find all Activities where the Phase with Name "Preplanning" exists.
To finish your query you need to add a select clause.
var query = from a in entities.Activities
join p in entities.Phases on a.PhaseId equals p.Id
where p.Name == "Preplanning"
select a.Name
will return IEnumerable<string> of all activity names.
Just select activity, as you want:
var query = from a in entities.Activities
join p in entities.Phases on a.PhaseId equals p.Id
where p.Name == "Preplanning"
select a;
Here is how query expression should look like:
A query expression must begin with a from clause and must end with a select or group clause. Between the first from clause and the last select or group clause, it can contain one or more of these optional clauses: where, orderby, join, let and even additional from clauses. You can also use the into keyword to enable the result of a join or group clause to serve as the source for additional query clauses in the same query expression.
Same as puzzling image:
With method syntax you don't need to end query with something special:
var query = entities.Phases
.Where(p => p.Name == "Preplanning")
.Join(entities.Activities, p => p.Id, a => a.PhaseId, (p,a) => a);
No need to do a join if you only need data from one of the tables. You can apply a filter instead:
var q = entities.Activities.Where(a =>
entities.Phases.Any(p => a.PhaseId == p.Id && p.Name == "Preplanning"));
I'm using the Massive Query method to write a simple join query against an Oracle database. This is my code with the query simplified even further by taking out some columns:
dynamic logTable = new DynamicModel("mydatabase", "table1");
var sb = new StringBuilder();
sb.Append("select CONTACT_ID from table1 inner join table2 on table1.ID = table2.ID ");
sb.Append("where table1.ID=:0");
dynamic dbResult = logTable.Query(sb.ToString(), id);
The following code gives me an error: 'object' does not contain a definition for 'CONTACT_ID'
string id = dbResult.CONTACT_ID.ToString();
If I take the exact query and run it through sqldeveloper, I get back the expected results. If I try to Query through Massive without a join, I get back an object I can work with.
Any ideas?
My mistake! I was expecting my query to return only one record, but forgot that Query returns IEnumerable. Solution is to take First() or loop over the results.
I have this SQL query:
SELECT Sum(ABS([Minimum Installment])) AS SumOfMonthlyPayments FROM tblAccount
INNER JOIN tblAccountOwner ON tblAccount.[Creditor Registry ID] = tblAccountOwner.
[Creditor Registry ID] AND tblAccount.[Account No] = tblAccountOwner.[Account No]
WHERE (tblAccountOwner.[Account Owner Registry ID] = 731752693037116688)
AND (tblAccount.[Account Type] NOT IN
('CA00', 'CA01', 'CA03', 'CA04', 'CA02', 'PA00', 'PA01', 'PA02', 'PA03', 'PA04'))
AND (DATEDIFF(mm, tblAccount.[State Change Date], GETDATE()) <=
4 OR tblAccount.[State Change Date] IS NULL)
AND ((tblAccount.[Account Type] IN ('CL10','CL11','PL10','PL11')) OR
CONTAINS(tblAccount.[Account Type], 'Mortgage')) AND (tblAccount.[Account Status ID] <> 999)
I have created a Linq query:
var ownerRegistryId = 731752693037116688;
var excludeTypes = new[]
{
"CA00", "CA01", "CA03", "CA04", "CA02",
"PA00", "PA01", "PA02", "PA03", "PA04"
};
var maxStateChangeMonth = 4;
var excludeStatusId = 999;
var includeMortgage = new[] { "CL10", "CL11", "PL10", "PL11" };
var sum = (
from account in context.Accounts
from owner in account.AccountOwners
where owner.AccountOwnerRegistryId == ownerRegistryId
where !excludeTypes.Contains(account.AccountType)
where account.StateChangeDate == null ||
(account.StateChangeDate.Month - DateTime.Now.Month)
<= maxStateChangeMonth
where includeMortgage.Contains(account.AccountType) ||
account.AccountType.Contains("Mortgage")
where account.AccountStatusId != excludeStatusId
select account.MinimumInstallment).ToList()
.Sum(minimumInstallment =>
Math.Abs((decimal)(minimumInstallment)));
return sum;
Are they equal/same ? I dont have records in db so I cant confirm if they are equal. In SQL there are brackets() but in Linq I didnt use them so is it ok?
Please suggest.
It is not possible for us to say anything about this, because you didn't show us the DBML. The actual definition of the mapping between the model and the database is important to be able to see how this executes.
But before you add the DBML to your question: we are not here to do your work, so here are two tips to find out whether they are equal or not:
Insert data in your database and run the queries.
Use a SQL profiler and see what query is executed by your LINQ provider under the covers.
If you have anything more specific to ask, we will be very willing to help.
The brackets will be generated by LINQ provider, if necessary.
The simplest way to check if the LINQ query is equal to the initial SQL query is to log it like #Atanas Korchev suggested.
If you are using Entity Framework, however, there is no Log property, but you can try to convert your query to an ObjectQuery, and call the ToTraceString method then:
string sqlQuery = (sum as ObjectQuery).ToTraceString();
UPD. The ToTraceString method needs an ObjectQuery instance for tracing, and the ToList() call already performs materialization, so there is nothing to trace. Here is the updated code:
var sum = (
from account in context.Accounts
from owner in account.AccountOwners
where owner.AccountOwnerRegistryId == ownerRegistryId
where !excludeTypes.Contains(account.AccountType)
where account.StateChangeDate == null ||
(account.StateChangeDate.Month - DateTime.Now.Month)
<= maxStateChangeMonth
where includeMortgage.Contains(account.AccountType) ||
account.AccountType.Contains("Mortgage")
where account.AccountStatusId != excludeStatusId
select account.MinimumInstallment);
string sqlQuery = (sum as ObjectQuery).ToTraceString();
Please note that this code will not perform the actual query, it is usable for testing purposes only.
Check out this article if you are interested in ready-for-production logging implementation.
There can be a performance difference:
The SQL query returns a single number (SELECT Sum...) directly from the database server to the client which executes the query.
In your LINQ query you have a greedy operator (.ToList()) in between:
var sum = (...
...
select account.MinimumInstallment).ToList()
.Sum(minimumInstallment =>
Math.Abs((decimal)(minimumInstallment)));
That means that the query on the SQL server does not contain the .Sum operation. The query returns a (potentially long?) list of MinimumInstallments. Then the .Sum operation is performed in memory on the client.
So effectively you switch from LINQ to Entities to LINQ to Objects after .ToList().
BTW: Can you check the last proposal in your previous question here which would avoid .ToList() on this query (if the proposal should work) and would therefore be closer to the SQL statement.