we have 4 entities:
Bills
BillDetails
Products
ProductGroups
what I want to do is something like this
var qry = from bill in ctx.Bills
join billDetail in ctx.BillDetails on bill.Id equal billDetail.Bill_Id
join product in ctx.Products on billDetail.Product_Id equals product.Id
join productGroup in ctx.ProductGroups
on product.ProductGroup_Id equals productGroup.Id
where
productGroup.Id == 113
select bill;
The problem is if we disable lazy loading the returned bill dos not contains BillDetail entity,
we have to return it explicitly as anonymous object.
Is there any way to convert it to something like this ?
var qry = ctx.Bills
.Include("BillDetails.Products.ProductGroup")
.where(s=>s.BillDetails.Products.ProductGroup.Id == 113);
Not 100% what you need, but something like this may work:
var qry = ctx.Bills
.Include("BillDetails.Products.ProductGroup")
.SelectMany(b => b.BillDetails)
.Where(bd => bd.Product.ProductGroup.Id == 113);
Related
A newbie asks...
Part 1
Suppose I have 3 classes (and their equivalent SQL tables) :
Product
{
int Id;
List<Keyword> Keywords;
List<Serial> Serials;
}
Keyword
{
int Id;
int ProductId; // FK to Product
string Name;
}
Serial
{
int Id;
int ProductId; // FK to Product
string SerialNumber;
}
When loading PRODUCT == 123, the we could do this:
item = db.Products.FirstOrDefault(p => p.Id == 123);
item.Keywords = db.Keywords.Where(p => p.ProductId == 123).ToList();
item.Serials = db.Serials.Where(p => p.ProductId == 123).ToList();
which is 3 SQL statements.
Or we could do this:
from product in db.Products.AsNoTracking()
join link1 in Db.Keywords.AsNoTracking()
on product.Id equals link1.ProductId into kwJoin
from keyword in kwJoin.DefaultIfEmpty()
join link2 in Db.Serials.AsNoTracking()
on product.Id equals link2.ProductId into serJoin
from serial in serJoin.DefaultIfEmpty()
where product.Id == 123
select new { product, keyword, serial };
which gives 1 SQL statement but produces far too many rows (number of keywords x number of serials) that need to be coalesced together
Both seem less than efficient. Is there a better way?
Part 2
As another question, but using the same example, when we have a join like so:
from product in db.Products.AsNoTracking()
join link1 in Db.Keywords.AsNoTracking()
on product.Id equals link1.ProductId into kwJoin
from keyword in kwJoin.DefaultIfEmpty()
select new { product, keyword };
Is there a way to assign the keywords directly in the product, in select statement?
select new { product, product.Keywords = keyword };
Thanks for any help!
If the FKs exist, depending on how you have setup your DB context, the properties will automatically be fetched. No joins required. Part 1 query is simple as it has a filter. Part 2 might have issues depending on how many records needs to be fetched from the database. You can map the fields to anonymous objects(or DTOs) after the fact that you have keyword objects for each product in the list.
Part 1
item = db.Products
.Include(p=>p.Keywords)
.Include(s=>s.Serials)
.Where(p => p.Id == 123)
.FirstOrDefault();
Part 2
products = db.Products.Include(p=>p.Keywords).ToList();
I have a condition where joining table have a condition. Let's say I have a table called Mapper Student Teacher where Mapper table have a column named AcNoId which contains a id from both table Student and Teacher. The table structure is
Mapper
Student
Teacher
TestOption is a enum and is defined as a
public enum TestOption
{
Teacher = 1,
Student = 2
}
Now I have a condition where if TestOption is a type of Student it should perform a join with Student table and if is a type of Teacher it should perform a join with Teacher table
This is how I have tried so far
(from m in _context.Mapper
where m.TestOption == TestOption.Student
join s in _context.Student
on m.AcNoId equals s.Id into tempStudent
from st in tempStudent.DefaultIfEmpty()
where m.TestOption == TestOption.Teacher
join t in _context.Teacher
on m.AcNoId equals t.Id into tempTeacher
from ta in tempTeacher.DefaultIfEmpty()
select new
{
Type = m.TestOption.ToString(),
Student = st.StudentName ?? string.Empty,
Teacher = ta.TeacherName ?? string.Empty
}).ToList();
Instead of conditional join this query perform a following query on SQL Profiler
exec sp_executesql N'SELECT [m].[TestOption], COALESCE([s].[StudentName], #__Empty_0) AS [Student], COALESCE([t].[TeacherName], #__Empty_1) AS [Teacher]
FROM [Mapper] AS [m]
LEFT JOIN [Student] AS [s] ON [m].[AcNoId] = [s].[Id]
LEFT JOIN [Teacher] AS [t] ON [m].[AcNoId] = [t].[Id]
WHERE ([m].[TestOption] = 2) AND ([m].[TestOption] = 1)',N'#__Empty_0 nvarchar(4000),#__Empty_1 nvarchar(4000)',#__Empty_0=N'',#__Empty_1=N''
How can I do this????
You can use the below code, with no need to use join or where statements on _context.Mapper:
(from m in _context.Mapper
select new
{
Type = m.TestOption.ToString(),
Student = _context.Student
.FirstOrDefault(s =>
m.TestOption == TestOption.Student &&
s.Id == m.AcNoId) ?? string.Empty,
Teacher = _context.Teacher
.FirstOrDefault(t =>
m.TestOption == TestOption.Teacher &&
t.Id == m.AcNoId) ?? string.Empty,
})
.ToList();
I'm trying to learn EF Core and hit this wall since I'm also fairly new to LINQ
Consider the model:
I'm trying to get all the distinct users from a single company;
The SQL statement would be something like this:
SELECT DISTINCT gau.AppUserId, au.Name, au.Id FROM Companies c
INNER JOIN Groups g ON g.CompanyId = c.Id
INNER JOIN GroupAppUsers gau ON gau.GroupId = g.Id
INNER JOIN AppUsers au ON gau.AppUserId = au.Id
Where c.Id = 40
Result:
How would I build this query like this? (Without the includes)
return await context.Companies
.Include(g => g.Groups)
.ThenInclude(au => au.AppUsers)
.ThenInclude(u => u.AppUser)
.SingleOrDefaultAsync(x => x.Id == id);
*Also, I'm not sure about the DB Model, I'm trying to avoid circular references but I think I should put Users linked with Companies instead of Groups, what do you think??
I'm trying to get all the distinct users from a single company
Rather than starting from companies and navigating to users, thus multiplying the users due to many-to-many relationship and then applying Disctinct operator, you could simply start from users and apply Any based criteria, thus eliminating the need of Disctinct at all.
Something like this (the DbSet / navigation property names could be different):
var companyUsers = await context.Users
.Where(u => u.UserGroups.Any(ug => ug.Group.Company.Id == id))
.ToListAsync();
Assuming your linking table (GroupAppUser) isn't modeled as an entity, something like:
var q = from c in db.Companies
from g in c.Groups
from u in g.AppUsers
select u;
or in Lambda form:
var q = db.Companies
.SelectMany(c => c.Groups)
.SelectMany(g => g.AppUsers);
Once you have the single Companies object, you can use the Navigation properties to get the AppUser objects:
return await context.Companies
.Include(g => g.Groups)
.ThenInclude(au => au.AppUsers)
.ThenInclude(u => u.AppUser)
.SingleOrDefaultAsync(x => x.Id == id)
.Groups.AppUsers.Distinct();
I'm trying to translate a query from raw sql to linq statement in EF Core 2
Query is something like this
SELECT * FROM TableA
WHERE FieldA = ConditionA
AND FieldB IN (SELECT FieldC FROM TableB WHERE FieldD = ConditionB)
FieldA and FieldB are from TableA, FieldC and FieldD are from TableB
I need all fields from TableA and none from TableB returned, so it should be something like
return Context.TableA
.Where(x => x.FieldA == ConditionA)
.[ some code here ]
.ToList()
my current solution is to get two distinct result sets and join them in code, something like this
var listA = Context.TableA
.Where(x => x.FieldA == ConditionA).ToList();
var listB = Context.TableB
.Where(x => x.FieldD == ConditionB).Select(x => x.FieldC).ToList();
listA.RemoveAll(x => !listB.Contains(x.FieldB);
return listA;
i hope it works, i still have to run tests on it, but i'm looking for a better solution (if anything exists)
You can simply use Contains function in query like this :
var ids = Context.TableB
.Where(p => p.FieldD == conditionD)
.Select(p => p.FieldC);
var result = Context.TableA
.Where(p => ids.Contains(p.FieldB))
.ToList();
It's a simple join that needs to be applied -
var result = (from a in Context.TableA.Where(x => x.FieldA == ConditionA )
join b in Context.TableB.Where(x => x.FieldD == ConditionB) on a.FieldB equals b.FieldC
select new {a}
).ToList();
I'm trying to write a query for a database that will left join a table to a look up table and the results will be returned based on a case statement.
In normal SQL the query would look like this:
SELECT chis_id, chis_detail, cilt.mhcatID, cilt.mhtID, 'TheFileName' =
CASE
WHEN cilt.mhcatID IS NOT NULL AND cilt.mhtID IS NOT NULL THEN chis_linked_filename
END
FROM chis
LEFT JOIN cilt on cilt.mhcatID = chis.mhcat_id AND cilt.mhtID = chis.mht_id
WHERE cch_id = 50
chis is the table being queried, cilt is a look-up table and does not contain any foreign key relationships to chis as a result (chis has existing FK's to mht and mhcat tables by the mhtID and mhcatID respectively).
The query will be used to return a list of history updates for a record. If the join to the cilt lookup table is successful this means that the caller of the query will have permission to view the filename of any associated files for the history updates.
Whilst during my research I've found various posts on here relating on how to do case statements and left joins in Linq to Entity queries, I've not been able to work out how to join on two different fields. Is this possible?
You need to join on an anonymous type with matching field names like so:
var query = from x in context.Table1
join y in context.Table2
on new { x.Field1, x.Field2 } equals new { y.Field1, y.Field2 }
select {...};
A full working example using the an extra from instead of a join would look something like this:
var query = from chis in context.Chis
from clit in context.Clit
.Where(x => x.mhcatID = chis.mhcat_id)
.Where(x => x.mhtID = chis.mht_id)
.DefaultIfEmpty()
select new
{
chis.id,
chis.detail,
cilt.mhcatID,
cilt.mhtID,
TheFileName = (cilt.mhcatID != null && cilt.mhtID != null) ? chis.linked_filename : null
};
Based on what Aducci suggested, I used a group join and DefaultIsEmpty() to get the results I wanted. For some reason, I couldn't get DefaultIfEmpty() didn't work correctly on its own and the resulting SQL employed an inner join instead of a left.
Here's the final code I used to get the left join working:
var query = (from chis in context.chis
join cilt in context.cilts on new { MHT = chis.mht_id, MHTCAT = chis.mhcat_id } equals new { MHT = cilt.mhtID, MHTCAT = cilt.mhcatID } into tempCilts
from tempCilt in tempCilts.DefaultIfEmpty()
where chis.cch_id == 50
select new {
chisID = chis.chis_id,
detail = chis.chis_detail,
filename = chis.chis_linked_filename,
TheFileName = (tempCilt.mhcatID != null && tempCilt.mhtID != null ? chis.chis_linked_filename : null),
mhtID = chis.mht_id,
mhtcatID = chis.mhcat_id
}).ToList();