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.
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 am trying to get a list of a database table called oracleTimeCards whose employee id equals to the employeeID in employees list. Here is what I wrote:
LandornetSQLEntities db = new LandornetSQLEntities();
List<OracleEmployee> employees = db.OracleEmployees.Where(e => e.Office.Contains(officeName) && e.IsActive == true).Distinct().ToList();
var oracleTimeCards = db.OracleTimecards.Where(c => employees.Any(e => c.PersonID == e.PersonID)).ToList();
Anyone has any idea?
I'm going to assume you're using Entity Framework here. You can't embed calls to arbitrary LINQ extension methods inside your predicate, since EF might not know how to translate these to SQL.
Assuming you want to find all the timecards for the employees you found in your first query, you have two options. The simplest is to have a navigation property on your Employee class, named let's say TimeCards, that points to a collection of time card records for the given employee. Here's how that would work:
var oracleTimeCards = employees
.SelectMany(e => e.TimeCards)
.ToList();
If you don't want to do this for whatever reason, you can create an array of employee IDs by evaluating your first query, and use this to filter the second:
var empIDs = employees
.Select(e => e.PersonID)
.ToArray();
var oracleTimeCards = db.OracleTimecards
.Where(tc => empIDs.Contains(tc.PersonID))
.ToList();
This question already has answers here:
EntityFramework - contains query of composite key
(12 answers)
Closed 2 years ago.
I have a table as follows:
PersonalDetails
Columns are:
Name
BankName
BranchName
AccountNo
Address
I have another list that contains 'Name' and 'AccountNo'.
I have to find all the records from table that whose respective 'Name' and 'AccountNo' are present in given list.
Any suggestion will be helpful.
I have done following but not of much use:
var duplicationhecklist = dataAccessdup.MST_FarmerProfile
.Join(lstFarmerProfiles,
t => new { t.Name,t.AccountNo},
t1 => new { t1.Name, t1.AccountNo},
(t, t1) => new { t, t1 })
.Select(x => new {
x.t1.Name,
x.t1.BankName,
x.t1.BranchName,
x.t1.AccountNo
}).ToList();
where lstFarmerProfiles is a list.
You probably found out that you can't join an Entity Framework LINQ query with a local list of entity objects, because it can't be translated into SQL. I would preselect the database data on the account numbers only and then join in memory.
var accountNumbers = lstFarmerProfiles.Select(x => x.AccountNo).ToArray();
var duplicationChecklist =
from profile in dataAccessdup.MST_FarmerProfile
.Where(p => accountNumbers
.Contains(p.AccountNo))
.AsEnumerable() // Continue in memory
join param in lstFarmerProfiles on
new { profile.Name, profile.AccountNo} equals
new { param.Name, param.AccountNo}
select profile
So you will never pull the bulk data into memory but the smallest selection you can probably get to proceed with.
If accountNumbers contains thousands of items, you may consider using a better scalable chunky Contains method.
Since you have the lists in .net of values you want to find, try to use the Contains method, for sample:
List<string> names = /* list of names */;
List<string> accounts = /* list of account */;
var result = db.PersonalDetails.Where(x => names.Contains(x.Name) && accounts.Contains(x.AccountNo))
.ToList();
If MST_FarmerProfile is not super large I think you best option is to bring it into memory using AsEnumerable() and do the joining there.
var duplicationhecklist =
(from x in dataAccessdup.MST_FarmerProfile
.Select(z => new {
z.Name,
z.BankName,
z.BranchName,
z.AccountNo
}).AsEnumerable()
join y in lstFarmerProfiles
on new { x.Name, x.AccountNo} equals new { y.Name, y.AccountNo}
select x).ToList();
Since data is usually located on different machines or in separate processes at least: DB - is one and your in-memory list is your app, there is just 2 ways to do it.
Download as small data part from DB to local as possible and join locally (usually using AsEnumerable() or basically ToList()). You got many good thoughts on this in other answers.
Another one is different - upload your local data to server somehow and perform query on DB side. Uploading can be done differently: using some temp tables OR using VALUES. Fortunately there is a small extension for EF now (for both EF6 and EF Core) which you could try. It is EntityFrameworkCore.MemoryJoin (name might be confusing, but it supports both EF6 and EF Core). As stated in author's article it modifies SQL query passed to server and injects VALUES construction with data from your local list. And query is executed on DB server.
If accountNo identifies the record then you could use:
var duplicationCheck = from farmerProfile in dataAccessdup.MST_FarmerProfile
join farmerFromList in lstFarmerProfiles
on farmerProfile.AccountNo equals farmerFromList.AccountNo
select new {
farmerProfile.Name,
farmerProfile.BankName,
farmerProfile.BranchName,
farmerProfile.AccountNo
};
If you need to join on name and account then this should work:
var duplicationCheck = from farmerProfile in dataAccessdup.MST_FarmerProfile
join farmerFromList in lstFarmerProfiles
on new
{
accountNo = farmerProfile.AccountNo,
name = farmerProfile.Name
}
equals new
{
accountNo = farmerFromList.AccountNo,
name = farmerFromList.Name
}
select new
{
farmerProfile.Name,
farmerProfile.BankName,
farmerProfile.BranchName,
farmerProfile.AccountNo
};
If you are only going to go through duplicateChecklist once then leaving .ToList() out will be better for performance.
I'm trying to use LINQ to query the following Entity Data Model
based on this db model
I'd like to be able to pull a list of products based on ProductFacets.FacetTypeId.
Normally, I'd use joins and this wouldn't be a problem but I don't quite understand how to query many-to-many tables under the Entity DataModel.
This is an example sql query:
select p.Name, pf.FacetTypeId from Products p
inner join ProductFacets pf on p.ProductId = pf.ProductId
where pf.FacetTypeId in(8, 12)
Presuming EF 4:
var facetIds = new [] { 8, 12 };
var q = from p in Context.Products
where p.FacetTypes.Any(f => facetIds.Contains(f.FacetTypeId))
select p;
In EF (assuming the mapping is done correctly), joins are hardly ever used; navigation properties are used instead.
Your original SQL returns a tuple with repeated Name entries. With LINQ, it's often easier
to "shape" the queries into non-tuple results.
The following should be the same as the SQL, only instead of returning (Name, FacetTypeId) pairs with repeated Names, it will return a type that has a Name and a sequence of FacetTypeIds:
var facetIds = new [] { 8, 12 };
var result = from p in db.Products
select new
{
p.Name,
FacetTypeIds = from pf in p.FacetTypes
where pf.FacetTypeId == 8 || pf.FacetTypeId == 12
select pf.FacetTypeId,
};
Suppose I have three tables:
Person(pid, ...)
PersonAddress(pid, aid,...)
Address(aid, ...)
Then I want to get the person address like sql:
select a.* from address a join PersonAddress pa on a.addressID=pa.addressID
where pa.personID = myPersonID
Use Entity Framework to create Entity model, then want to write a linq equivalent as above sql.
I tried it in following way:
var addresses = this.GetAddress();
var personaddresses = this.GetPersonAddress();
var query = from ad in addresses
from pa in personaddresses
where ((ad.AddressID == pa.AddressID)&&(pa.PersonID==person.personID))
select ad;
but I got error. Or I try to start from:
var result = this.Context.Address;
var result = result.Join .... //how to write linq in this way?
How to write the linq?
This is untested but if you have all of your relationships setup and you create the model (I have used Model as the name for this) from this you should be able to use the following:
var values = this.Model.Address.Select(a => a.PersonAddress.Where(pa => pa.Id == myPersonID));
You almost never use join in LINQ to Entities.
Try:
var q = from p in Context.People
where p.PersonId == personId
from a in p.Addresses // presumes p.Addresses is 1..*
select a;
Assuming you have three entities: Person, PersonAddress and Address, here is a query that should meet your needs (this example assumes an Entity Framework context named context):
var values = context.PersonAddress.Where(pa => pa.Person.PersonId == myPersonId).Select(pa => pa.Address);
However, if the PersonAddress table exists as a pure many-to-many relationship table (i.e. contains only keys), you'd be better off setting up your Entity Framework model in such a way that the intermediate table isn't necessary, which would leave you with the much simpler:
var values = context.Person.Where(p => p.PersonId == myPersonId).Addresses;
Based on the additional feedback
Because you need to include the country table, you should originate your query from the Address table. In that case:
var values = context.Address.Where(a => a.PersonAddress.Where(pa => pa.Product.Id == myProductId).Count() > 0)
To include the Country table in the result:
var values = context.Address.Include("Country").Where(a => a.PersonAddress.Where(pa => pa.Product.Id == myProductId).Count() > 0)