I have tables association such as (CaseClient is a bridge table):
Cases has many CaseClients
Client has many CaseClients
ClientType has many CaseClient
The easiest way just use the view in database but I heard that with linq you can join this somehow? Or should I just created view in the database and linq query agains that view?
I am appreciated your comment
I think you want to use the Join method, from your bridging table and resolving each of your relationships. E.g.
// Where CaseId and TypeId are your members of CaseClient
var x = caseClients.Join( cases, cc => cc.CaseId, c => c.Id)
.Join( types, cc => cc.TypeId, t => t.Id)
.Select();
Above code untested (so far) and from memory. You may need to put a Select between the two joins.
Heres an adaptation of what I did for a very similar situation. Only the names have been changed to protect the innocent.
IEnumerable<Case> getCaseByClient(int client_id)
{
var ret = from c in Cases
join cc in CasesClients
on c.Id equals cc.ClientId
join cl in Clients
on cc.ClientId equals client_id
select c;
return ret;
}
of course this assumes your client_id field is an int, but thats easy enough to modify.
Related
I have the following LINQ query (using EF Core 6 and MS SQL Server):
var resultSet = dbContext.Systems
.Include(system => system.Project)
.Include(system => system.Template.Type)
.Select(system => new
{
System = system,
TemplateText = system.Template.TemplateTexts.FirstOrDefault(templateText => templateText.Language == locale.LanguageIdentifier),
TypeText = system.Template.Type.TypeTexts.FirstOrDefault(typeText => typeText.Language == locale.LanguageIdentifier)
})
.FirstOrDefault(x => x.System.Id == request.Id);
The requirement is to retrieve the system matching the requested ID and load its project, template and template's type info. The template has multiple TemplateTexts (one for each translated language) but I only want to load the one matching the requested locale, same deal with the TypeTexts elements of the template's type.
The LINQ query above does that in one query and it gets converted to the following SQL query (I edited the SELECT statements to use * instead of the long list of columns generated):
SELECT [t1].*, [t2].*, [t5].*
FROM (
SELECT TOP(1) [p].*, [t].*, [t0].*
FROM [ParkerSystems] AS [p]
LEFT JOIN [Templates] AS [t] ON [p].[TemplateId] = [t].[Id]
LEFT JOIN [Types] AS [t0] ON [t].[TypeId] = [t0].[Id]
LEFT JOIN [Projects] AS [p0] ON [p].[Project_ProjectId] = [p0].[ProjectId]
WHERE [p].[SystemId] = #__request_Id_1
) AS [t1]
LEFT JOIN (
SELECT [t3].*
FROM (
SELECT [t4].*, ROW_NUMBER() OVER(PARTITION BY [t4].[ReferenceId] ORDER BY [t4].[Id]) AS [row]
FROM [TemplateTexts] AS [t4]
WHERE [t4].[Language] = #__locale_LanguageIdentifier_0
) AS [t3]
WHERE [t3].[row] <= 1
) AS [t2] ON [t1].[Id] = [t2].[ReferenceId]
LEFT JOIN (
SELECT [t6].*
FROM (
SELECT [t7].*, ROW_NUMBER() OVER(PARTITION BY [t7].[ReferenceId] ORDER BY [t7].[Id]) AS [row]
FROM [TypeTexts] AS [t7]
WHERE [t7].[Language] = #__locale_LanguageIdentifier_0
) AS [t6]
WHERE [t6].[row] <= 1
) AS [t5] ON [t1].[Id0] = [t5].[ReferenceId]
which is not bad, it's not a super complicated query, but I feel like my requirement can be solved with a much simpler SQL query:
SELECT *
FROM [Systems] AS [p]
JOIN [Templates] AS [t] ON [p].[TemplateId] = [t].[Id]
JOIN [TemplateTexts] AS [tt] ON [p].[TemplateId] = [tt].[ReferenceId]
JOIN [Types] AS [ty] ON [t].[TypeId] = [ty].[Id]
JOIN [TemplateTexts] AS [tyt] ON [ty].[Id] = [tyt].[ReferenceId]
WHERE [p].[SystemId] = #systemId and tt.[Language] = 2 and tyt.[Language] = 2
My question is: is there a different/simpler LINQ expression (either in Method syntax or Query syntax) that produces the same result (get all info in one go) because ideally I'd like to not have to have an anonymous object where the filtered sub-collections are aggregated. For even more brownie points, it'd be great if the generated SQL would be simpler/closer to what I think would be a simple query.
Is there a different/simpler LINQ expression (...) that produces the same result
Yes (maybe) and no.
No, because you're querying dbContext.Systems, therefore EF will return all systems that match your filter, also when they don't have TemplateTexts etc. That's why it has to generate outer joins. EF is not aware of your apparent intention to skip systems without these nested data or of any guarantee that these systems don't occur in the database. (Which you seem to assume, seeing the second query).
That accounts for the left joins to subqueries.
These subqueries are generated because of FirstOrDefault. In SQL it always requires some sort of subquery to get "first" records of one-to-many relationships. This ROW_NUMBER() OVER construction is actually quite efficient. Your second query doesn't have any notion of "first" records. It'll probably return different data.
Yes (maybe) because you also Include data. I'm not sure why. Some people seem to think Include is necessary to make subsequent projections (.Select) work, but it isn't. If that's your reason to use Includes then you can remove them and thus remove the first couple of joins.
OTOH you also Include system.Project which is not in the projection, so you seem to have added the Includes deliberately. And in this case they have effect, because the entire entity system is in the projection, otherwise EF would ignore them.
If you need the Includes then again, EF has to generate outer joins for the reason mentioned above.
EF decides to handle the Includes and projections separately, while hand-crafted SQL, aided by prior knowledge of the data could do that more efficiently. There's no way to affect that behavior though.
This LINQ query is close to your SQL, but I'm afraid of correctness of the result:
var resultSet =
(from system in dbContext.Systems
from templateText in system.Template.TemplateTexts
where templateText.Language == locale.LanguageIdentifier
from typeText in system.Template.Type.TypeTexts
where typeText.Language == locale.LanguageIdentifier
select new
{
System = system,
TemplateText = templateText
TypeText = typeText
})
.FirstOrDefault(x => x.System.Id == request.Id);
I have a performance issue with the API. It is due to retrieving data from multiple tables like below
Example:
Users.Include(x => x.UsersAdditionInfo)
.Include(x => x.UserRoles)
.Include(x => x.Location)
Note: each of these tables contains nearly (1,50,000) records except location table.
I have used joins instead of .Include then also facing the same performance issues.
Example:
from ub in users
join ua in UserAdditionalInfo on ub.Id equals ua.UserId
join ur in UserRoles on ub.Id equals ur.UserId
join urs in userRoles on ur.RoleId equals urs.Id
join l in Location on ub.LocationId equals l.Id
into leftLocation
from location in leftLocation.DefaultIfEmpty()
Kindly suggest for better alternative ways to query in multiple tables
If your EDMX is probably configured, you don't have to join yourself.
Can't you just do
Users.Select(x=> new {
UserRoles = x.UserRoles,
UserAdditionInfo = x.UserAdditionInfo,
Location = x.Location })
and so on?
(I've fudged your schema a bit but hopefully you get my point)
Also, if this is common, you could also always create a view in SQL Server and add it in EDMX
I have the source code like this:
var res = from s in Splitting
join c in Customer on s.CustomerId equals c.Id
where c.Id == customrId
&& c.CompanyId == companyId
select s;
When reviewing code, one member said that my code applies for only one SQL db, and advised me to use LinQ to Entity with Join so that it will work for all databases.
I don't understand, I think, even with other db, we will add it to Entity Framework. And the code below will work correct too, right?
Please advise.
There are two ways you can write your LINQ.
1.LINQ Query Expressions (query-syntax) (Which you have done)
var res = from s in Splitting
join c in Customer on s.CustomerId equals c.Id
where c.Id == customrId
&& c.CompanyId == companyId
select s;
2.Another is LINQ query extension methods (dot-syntax)
var res = Splitting.Join(Customer,
sp => sp.CustomerId,
cu => cu.Id,
(sp, cu) => new { sp, cu })
.Where(s => s.cu.Id == customrId && s.cu.CompanyId == companId)
.Select(s => s.sp);
For joins, I strongly prefer query-syntax.There are details that
query-syntax hides that can make it well worth embracing with the improvement to readability it brings.However query-syntax is somewhat
more limited than dot-syntax in other aspects.
dot-syntax is more concise but performing multiple table joins is a nightmare.The flip side is that there are a number of LINQ
operations that only exist within the dot-syntax: Single(),
First(), Count() etc.For these limitation of query-syntax you can use
dot-syntax.
N.B : At compile time, all are converted to Standard Query.
I'm porting some sql stored procedure logic, which would return multiple tables in a dataset, to entity framework strongly typed objects, queried with linq.
Basically I need the data from tables A, B, and C, where C has a foreign key to B, and B has a foreign key to A. But I don't want every C with a FK to B, just the C's with a certain constraint X.
So basically, the stored proc basically said
TableA = select from A where A.AID = AIDPassedIn
TableB = select from B where B.AID = AIDPassedIn
TableC = select from TableB where TableB.XID = XIDPassedIn
return new DataSet(TableA, TableB, TableC);
//yes this is gross and confusing, thus our current efforts
Entity framework almost makes this super easy like so
A.Include("B.C").Where(a => a.AID == AIDPassedIn)
My only problem is that this doesn't include constraint X on the C table. I've read a bunch of articles, but everything I've read suggests things I could add to the where clause, and that would filter what A objects I end up with. I should only end up with one A object though, regardless of the properties of it's children. What I want is The A with AIDPassedIn, and all it's child B's, and all the B's children C that match constraint X.
I feel like this is one of my worst phrased questions ever but I'm at a bit of a block. Any help would be great thanks!
You can try it along the lines of the following:
var AList = context.As.Where(a => a.AID == AIDPassedIn)
.Select(a => new
{
A = a,
Bs = a.Bs,
Cs = a.Bs.Select(b => b.Cs.Where(c => c.XID == XIDPassedIn))
})
.AsEnumerable()
.Select(x => x.A)
.ToList(); // or SingleOrDefault if AIDPassedIn is the PK
Entity Framework will put the object graph together automatically (even without using Include) as long as you don't disable change tracking.
I have this sql that i want to have written in linq extension method returning an entity from my edm:
SELECT p.[Id],p.[Firstname],p.[Lastname],prt.[AddressId],prt.[Street],prt.[City]
FROM [Person] p
CROSS APPLY (
SELECT TOP(1) pa.[AddressId],a.[ValidFrom],a.[Street],a.[City]
FROM [Person_Addresses] pa
LEFT OUTER JOIN [Addresses] AS a
ON a.[Id] = pa.[AddressId]
WHERE p.[Id] = pa.[PersonId]
ORDER BY a.[ValidFrom] DESC ) prt
Also could this be re-written in linq extension method using 3 joins?
Assuming you have set the Person_Addresses table up as a pure relation table (i.e., with no data besides the foreign keys) this should do the trick:
var persons = model.People
.Select(p => new { p = p, a = p.Addresses.OrderByDescending(a=>a.ValidFrom).First() })
.Select(p => new { p.p.Id, p.p.Firstname, p.p.LastName, AddressId = p.a.Id, p.a.Street, p.a.City });
The first Select() orders the addresses and picks the latest one, and the second one returns an anonymous type with the properties specified in your query.
If you have more data in your relation table you're gonna have to use joins but this way you're free from them. In my opinion, this is more easy to read.
NOTE: You might get an exception if any entry in Persons have no addresses connected to them, although I haven't tried it out.