Does anybody know how to convert this on outerjoin on LINQ Lambda?
I wan to achieve this using lambda linq
SELECT * FROM Posts as A LEFT JOIN Reactions as B on A.Id = B.PostId AND #userId = b.userid
Here is my current linq code
return await _dbContext.Posts
.GroupJoin(_dbContext.Reactions,
post => post.Id, reaction => reaction.PostId,
(post, reactions) => new { post, reactions })
.SelectMany(x => x.reactions.DefaultIfEmpty(),
(post, reaction) => new { post.post, reaction })
What you want to accomplish can be done in two different ways in SQL, and those ways can be translated to Linq.
Depending on your scenario (volume of data, indexes, etc) you may want to need one or another
Option A: Join the filtered data
SELECT a.Name, b.*
FROM
tableA
LEFT JOIN tableB on
b.Action='delete' AND a.Id = b.Id
would be translated in LINQ to something similar to:
var query =
from a in db.TableA
join pet in db.TableB.Where(x => x.Action=="delete") on a equals b.TableA into gj
from leftJoined in gj.DefaultIfEmpty()
and using method syntax:
var query = tableA
.GroupJoin(
tableB.Where(x => x.Action == "delete"),
tableA => tableA,
tableB => tableB.tableA,
(tableA, tableBs) => new {tableA, tableBs}
).SelectMany(x => x.tableBs.DefaultIfEmpty())
Option B: Do the join and later filter the data
SELECT a.Name, b.*
FROM
tableA
LEFT JOIN tableB on a.Id = b.Id
WHERE
b.Id = NULL OR b.Action='delete'
would be translated to:
var query =
from a in db.TableA
join pet in db.TableB on a equals b.TableA into gj
from leftJoined in gj.DefaultIfEmpty()
where lefjoined == null || leftjoined.Action == "delete"
A left outer join is a join in which each element of the first collection is returned, regardless of whether it has any correlated elements in the second collection. You can use LINQ to perform a left outer join by calling the DefaultIfEmpty method on the results of a group join.
You can use this approach
Query Syntax:
var query = (from post in Posts
join reaction in Reactions
on post.Id equals reaction.PostId
into reaction
from reaction in reaction.DefaultIfEmpty()
select new
{
post.Id,
//prod.Foo1,
//post.Foo2,
//reaction.Foo3,
//reaction.Foo4,
//you can select other fields too
}).OrderBy(ps => ps.Id);
For more information visit Perform left outer joins
Normally you don't. Flattening out related data like that is simply not necessary in LINQ. Just fetch the data with its natural shape:
_dbContext.Posts.Include(p => p.Reactions)
This returns the Posts and any reactions, without having to repeat the Post data for each Reaction, or having nulls for Posts without Reactions.
I am trying to join three SQL tables in LINQ c# for the below SQL
SELECT
rpp.*
FROM dbo.Orgs ao
LEFT JOIN dbo.Afflia rpa
ON rpa.AccountId = ao.ID
INNER JOIN dbo.reports rpp
ON rpp.Id = rpa.reporttId
WHERE ao.Name like '%xyz%'
above query returns data but the equivalent LINQ query doesn't as in below
from a in context.Orgs
join aff in context.Afflia on a.ID equals aff.AccountId
join prescriber in context.Reports on aff.reportId equals prescriber.Id
where a.ORG_NAME.Contains("xyz")
May I know where the mistake is?
In LINQ you did INNER join but In SQL, you did LEFT join.
Try this instead:
from a in context.Orgs
join aff in context.Afflia on a.ID equals aff.AccountId into affs
from aff in affs.DefaultIfEmpty()
join prescriber in context.Reports on aff.reportId equals prescriber.Id
where a.ORG_NAME.Contains("xyz")
In your SQL you are doing a LEFT join to dbo.Afflia, but in your LINQ you are doing an inner join. You need to add "DefaultIfEmpty(), eg
from aff in context.Afflia.Where(join condition here).DefaultIfEmpty()
You could do:
var prescribers = (from a in context.Orgs
from aff in context.Afflia.Where(aff => aff.AccountId == a.ID)
from prescriber in context.Reports.Where(pres => pres.Id == aff.reportId)
where a.ORG_NAME.Contains("xyz")
select prescriber)
.ToList();
I'm writing a LINQ to SQL statement, and I'm after the standard syntax for a normal inner join with an ON clause in C#.
How do you represent the following in LINQ to SQL:
select DealerContact.*
from Dealer
inner join DealerContact on Dealer.DealerID = DealerContact.DealerID
It goes something like:
from t1 in db.Table1
join t2 in db.Table2 on t1.field equals t2.field
select new { t1.field2, t2.field3}
It would be nice to have sensible names and fields for your tables for a better example. :)
Update
I think for your query this might be more appropriate:
var dealercontacts = from contact in DealerContact
join dealer in Dealer on contact.DealerId equals dealer.ID
select contact;
Since you are looking for the contacts, not the dealers.
And because I prefer the expression chain syntax, here is how you do it with that:
var dealerContracts = DealerContact.Join(Dealer,
contact => contact.DealerId,
dealer => dealer.DealerId,
(contact, dealer) => contact);
To extend the expression chain syntax answer by Clever Human:
If you wanted to do things (like filter or select) on fields from both tables being joined together -- instead on just one of those two tables -- you could create a new object in the lambda expression of the final parameter to the Join method incorporating both of those tables, for example:
var dealerInfo = DealerContact.Join(Dealer,
dc => dc.DealerId,
d => d.DealerId,
(dc, d) => new { DealerContact = dc, Dealer = d })
.Where(dc_d => dc_d.Dealer.FirstName == "Glenn"
&& dc_d.DealerContact.City == "Chicago")
.Select(dc_d => new {
dc_d.Dealer.DealerID,
dc_d.Dealer.FirstName,
dc_d.Dealer.LastName,
dc_d.DealerContact.City,
dc_d.DealerContact.State });
The interesting part is the lambda expression in line 4 of that example:
(dc, d) => new { DealerContact = dc, Dealer = d }
...where we construct a new anonymous-type object which has as properties the DealerContact and Dealer records, along with all of their fields.
We can then use fields from those records as we filter and select the results, as demonstrated by the remainder of the example, which uses dc_d as a name for the anonymous object we built which has both the DealerContact and Dealer records as its properties.
var results = from c in db.Companies
join cn in db.Countries on c.CountryID equals cn.ID
join ct in db.Cities on c.CityID equals ct.ID
join sect in db.Sectors on c.SectorID equals sect.ID
where (c.CountryID == cn.ID) && (c.CityID == ct.ID) && (c.SectorID == company.SectorID) && (company.SectorID == sect.ID)
select new { country = cn.Name, city = ct.Name, c.ID, c.Name, c.Address1, c.Address2, c.Address3, c.CountryID, c.CityID, c.Region, c.PostCode, c.Telephone, c.Website, c.SectorID, Status = (ContactStatus)c.StatusID, sector = sect.Name };
return results.ToList();
You create a foreign key, and LINQ-to-SQL creates navigation properties for you. Each Dealer will then have a collection of DealerContacts which you can select, filter, and manipulate.
from contact in dealer.DealerContacts select contact
or
context.Dealers.Select(d => d.DealerContacts)
If you're not using navigation properties, you're missing out one of the main benefits on LINQ-to-SQL - the part that maps the object graph.
Use Linq Join operator:
var q = from d in Dealer
join dc in DealerConact on d.DealerID equals dc.DealerID
select dc;
basically LINQ join operator provides no benefit for SQL. I.e. the following query
var r = from dealer in db.Dealers
from contact in db.DealerContact
where dealer.DealerID == contact.DealerID
select dealerContact;
will result in INNER JOIN in SQL
join is useful for IEnumerable<> because it is more efficient:
from contact in db.DealerContact
clause would be re-executed for every dealer
But for IQueryable<> it is not the case. Also join is less flexible.
Actually, often it is better not to join, in linq that is. When there are navigation properties a very succinct way to write your linq statement is:
from dealer in db.Dealers
from contact in dealer.DealerContacts
select new { whatever you need from dealer or contact }
It translates to a where clause:
SELECT <columns>
FROM Dealer, DealerContact
WHERE Dealer.DealerID = DealerContact.DealerID
Inner join two tables in linq C#
var result = from q1 in table1
join q2 in table2
on q1.Customer_Id equals q2.Customer_Id
select new { q1.Name, q1.Mobile, q2.Purchase, q2.Dates }
Use LINQ joins to perform Inner Join.
var employeeInfo = from emp in db.Employees
join dept in db.Departments
on emp.Eid equals dept.Eid
select new
{
emp.Ename,
dept.Dname,
emp.Elocation
};
Try this :
var data =(from t1 in dataContext.Table1 join
t2 in dataContext.Table2 on
t1.field equals t2.field
orderby t1.Id select t1).ToList();
OperationDataContext odDataContext = new OperationDataContext();
var studentInfo = from student in odDataContext.STUDENTs
join course in odDataContext.COURSEs
on student.course_id equals course.course_id
select new { student.student_name, student.student_city, course.course_name, course.course_desc };
Where student and course tables have primary key and foreign key relationship
try instead this,
var dealer = from d in Dealer
join dc in DealerContact on d.DealerID equals dc.DealerID
select d;
var Data= (from dealer in Dealer join dealercontact in DealerContact on dealer.ID equals dealercontact.DealerID
select new{
dealer.Id,
dealercontact.ContactName
}).ToList();
var data=(from t in db.your tableName(t1)
join s in db.yourothertablename(t2) on t1.fieldname equals t2.feldname
(where condtion)).tolist();
var list = (from u in db.Users join c in db.Customers on u.CustomerId equals c.CustomerId where u.Username == username
select new {u.UserId, u.CustomerId, u.ClientId, u.RoleId, u.Username, u.Email, u.Password, u.Salt, u.Hint1, u.Hint2, u.Hint3, u.Locked, u.Active,c.ProfilePic}).First();
Write table names you want, and initialize the select to get the result of fields.
from d1 in DealerContrac join d2 in DealerContrac on d1.dealearid equals d2.dealerid select new {dealercontract.*}
One Best example
Table Names : TBL_Emp and TBL_Dep
var result = from emp in TBL_Emp join dep in TBL_Dep on emp.id=dep.id
select new
{
emp.Name;
emp.Address
dep.Department_Name
}
foreach(char item in result)
{ // to do}
In SQL I to get the distinct statement, I used join to get it as below
select distinct
col1
from
table1 a
inner join
table2 b on a.code = b.vcode
How can the same be implemented in LINQ over Entity Framework?
Please suggest me.
You can also use method syntax:
var query = table1.Join(table2,
a => a.code,
b => b.vcode,
(a,b) => a.col1)
.Distinct();
var result = (from a in table1
join b in table2 on a.code equals b.vcode
select a.col1).Distinct();
There are 3 tables: ParentCategories -> Categories -> Articles.
ParentCategory(ID, Name)
Category(ID, parentCategoryID, Name)
Article(ID, caregoryID, Name)
How do I select all articles with specified parentCategoryID (the table articles has only reference to categoreID, not to ParentCategoryID) using LINQ to SQL?
Something like this:
articles = (
from a in db.Articles
join c in db.Categories
on ????????????
join pc in db.ParentCategories
on c.ParentCategoryId equals pc.ID
...);
(If I understand your schema correctly) you could use an implicit join strategy like:
var articles = db.Categories
.Where(c => c.ParentCategoryID == yourParentCategoryID)
.SelectMany(c => c.Articles)
.ToList();
The implicit join requires that you have Associations set up between your entities in your O/R designer.
articles = from a in db.Articles
join c in db.Categories
on myParentCategoryID equals c.ParentCategoryId
select a;