Suppose I have 3 tables: A(aid, ...), B(bid, ...) Relationship(aid, bid, ...)
Then I have a aid as parameter, I want to get the result from b. If use SQL, will be like
select b.* from B join Relationship on b.bid = Relationship.bid
where relationship.aid = aid_param
how to write linq with same result as above SQL. (the foreign key was not created correctly in this case)?
Assuming that you've used the designer to add your tables to the LINQ data context and you have either foreign key relationships defined in the database or have hand-coded the associations in the designer, you should simply be able to reference the B table and it's EntitySet of Relationship properties, filtered by your parameter, and check if there are any matches.
var relationships = db.B.Any( b => b.Relationships.Where( r => r.aid == aid_param ) );
var bQuery = from r in MyContext.Relationship
where r.aid == aid_param
select r.B;
If you don't have a relationship set in the model, then u can:
var bQuery = from b in myContext.B
where myContext.Relationship
.Any( r => r.aid == aid_param && b.bid == r.bid)
select b;
var output =
from b
from Relationship
where (b.bid = Relationship.bid,
relationship.aid = aid_param)
Related
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 formed the following LINQ query, but it gives error
mcc_season is not an attribute in mcc_product
How do I form the query where I have 2 WHERE conditions and both from different entities in the join
var guestCardProduct =
(from c in CrmOrgServiceContext.mcc_productpriceSet
join d in CrmOrgServiceContext.mcc_productSet
on c.mcc_product.Id equals d.mcc_productId
where d.mcc_producttype.Value == (int)mcc_product.mcc_producttypeOptionSet.GuestCard
&& c.mcc_season.Id == seasonId
select new
{
d.mcc_productId,
c.mcc_price
}).FirstOrDefault();
You might be able to re-write it as follows:
var guestCardProduct =
(from c in CrmOrgServiceContext.mcc_productpriceSet
where c.mcc_season.Id == seasonId
join d in CrmOrgServiceContext.mcc_productSet
on c.mcc_product.Id equals d.mcc_productId
where d.mcc_producttype.Value == (int)c.mcc_product.mcc_producttypeOptionSet.GuestCard
select new
{
d.mcc_productId,
c.mcc_price
}).FirstOrDefault();
We're assuming here that there are 1 - 0..1 relationships between mcc_productpriceSet and both mcc_season and mcc_product and also a 1 - 0..1 relationship between mcc_product and mcc_producttypeOptionSet. If you have 1-n relationships between any of these, then you are going to have to work through those relationships rather than dotting into the single property because you will have collections of child objects rather than a single child object. You may find it helpful to break your query into smaller pieces to narrow down the source of the problem.
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,
};
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.
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)