Linq to SQL - Left Outer Join with Multiple Join Conditions

LINQ to SQL - Left Outer Join with multiple join conditions

You need to introduce your join condition before calling DefaultIfEmpty(). I would just use extension method syntax:

from p in context.Periods
join f in context.Facts on p.id equals f.periodid into fg
from fgi in fg.Where(f => f.otherid == 17).DefaultIfEmpty()
where p.companyid == 100
select f.value

Or you could use a subquery:

from p in context.Periods
join f in context.Facts on p.id equals f.periodid into fg
from fgi in (from f in fg
             where f.otherid == 17
             select f).DefaultIfEmpty()
where p.companyid == 100
select f.value

LInq left join with multiple condition in on clause

• If you really want to do it with a JOIN, you could do it like this:

  from cust in customer
  join _p1 in products on cust.identifier equals _p1.orgID into _p1
  from p1 in _p1.DefaultIfEmpty()
  join _p2 in products on cust.identifier equals _p2.personalno into _p2
  from p2 in _p2.DefaultIfEmpty()
  where cust.identifier != null
  && (p1 != null || p2 != null)
  select new { Customer = cust, Product = p1 == null ? p2 : p1 }
  

• An easier solution without the JOINkeyword would be:

  from p in products
  from cust.Where(q => q.identifier != null && (p.orgID == q.identifier || p.personalno == q.identifier)).DefaultIfEmpty()
  where cust != null
  select new { Product = p, Customer = cust }
  

• To answer the question, that the headline suggests, do the following to do a join on multiple conditions, but be aware, that this only works for AND conditions and not for OR conditions:

  from t1 in Table1
  join t2 in Table2 on new { Criteria1 = t1.criteria1, Criteria2 = t1.criteria2 } equals new { Criteria1 = t2.criteria1, Criteria2 = t2.criteria2 }
  select new { T1 = t1, T2 = t2 }
  

SQL to LINQ Left Outer Join with Multiple Conditions

This one should give you desired SQL:

.....
  join bn in applicationDbContext.Bins 
     on new { pr.ProdId, sz.size_id } equals new { bn.ProdId, bn.size_id } into ps                
  from bn in ps.DefaultIfEmpty()
  select new CoreBin
  {
    ... fields here
  }
.....

Multiple conditions on a left outer join clause in a LINQ query

With the help of the comments on the question, I've figured out writing the query using LINQ syntax.

from q in context.Questions
join qpph in context.PoolPickHandles
  on new { questionId = q.Id, pickerId = user.Id } 
    equals new { questionId = qpph.QuestionId, pickerId = qpph.PickerId } 
      into Handles
from m in Handles.DefaultIfEmpty()
where m == null
select q;

LINQ for an SQL with multiple LEFT OUTER JOINS on different tables

You can simply convert your query to linq query like this:

var results = (from a in A_TABLE
               join b in B_TABLE
               on a.A_TABLE_Id equals b.A_TABLE_Id into ab
               from b in ab.DefaultIfEmpty()
               join c in C_TABLE_List on b.B_TABLE_Id equals c.B_TABLE_Id

               select new
                   {
                     ClassAProperty1 = a.Property1,
                     ClassBProperty1 = b.Property1,
                     ClassCProperty1 = c.Property1
                   }).ToList();

you can continue on joining tables whatever times you need.

Don't forget to change Property# to required property names.

for more info take a look at LINQ Left Outer Join, and this stack thread.

Update:
this is the Lambda expressions version of the query:

var result = A_TABLE
             .GroupJoin(B_TABLE,
                 a => a.A_TABLE_Id,
                 b => b.A_TABLE_Id,
                 (a, b) =>
                 new {
                       tableAProperty1 = a.Property1,
                       tableAProperty2 = a.Property2, /* You cannot access this property in next join if you don't add it here */
                       B_TABLE = b.FirstOrDefault() /* This is the way to access B_TABLE in next join */
                 }).GroupJoin(C_TABLE,
                       ab => ab.B_TABLE.B_TABLE_Id,
                       c => c.B_TABLE_Id,
                       (ab, c) =>
                       new {
                             ab.tableAProperty1,
                             B_TABLEProperty2 = ab.B_TABLE.Property2,
                             C_TABLE = c.FirstOrDefault()
                            }).ToList();

LINQ Left Outer Join Multiple Tables with Group Count and Row Concatenation

Assuming you are using EF, and you have navigation properties set up, then your query would look like this:

var result = context.Parents
  .Select(p => new {
    p.ParentId,
    p.ParentName,
    p.ParentOccupation,
    NumberOfGrandChildren = p.Children
       .SelectMany(c => c.GrandChildren)
       .Count(),
    NamesOfGrandChildren = string.Join(", ", p.Children
      .SelectMany(c => c.GrandChildren)
      .Select(g => g.GrandChildName))
  }).ToList();

LINQ: Left Outer Join with multiple conditions

var items = inputReportDefinitions.GroupJoin(
              baseReportDefinitions,
              firstSelector => new {
                         firstSelector.ParentName, firstSelector.ReportName
                                   },
              secondSelector => new {
                         secondSelector.ParentName, secondSelector.ReportName
                                   },
              (inputReport, baseCollection) => new {inputReport, baseCollection})
              .SelectMany(grp => grp.baseCollection.DefaultIfEmpty(),
                         (col, baseReport) => new
                                                 {
                                                    Base = baseReport,
                                                    Input = col.inputReport
                                                 });

I believe this ends up being a left outer join. I don't know how to convert this monstrosity to a query statement. I think if you add AsQueryable() to the end it could be used in Linq-to-SQL, but honestly, I have little experience with that.

EDIT: I figured it out. Much easier to read:

var otherItems = from i in inputReportDefinitions
                         join b in baseReportDefinitions
                         on new {i.ParentName, i.ReportName} 
                         equals new {b.ParentName, b.ReportName} into other
                         from baseReport in other.DefaultIfEmpty()
                         select new
                                    {
                                        Input = i,
                                        Base = baseReport
                                    };

Complex joins in Linq with multiple tables and LEFT OUTER JOIN

You should apply Left Join this way:

join readers in db.Readers on readerdata.mac_address equals readers.mac_address into readersJ
from readers in readersJ.DefaultIfEmpty()

The full code:

var query = (
    from tags in db.Tags
    join tagreads in db.tag_reads on tags.epc equals tagreads.epc
    join readerdata in db.ReaderData on tagreads.ReaderDataId equals readerdata.Id
    join readers in db.Readers on readerdata.mac_address equals readers.mac_address into readersJ
    from readers in readersJ.DefaultIfEmpty()
    join locations in db.Locations 
        on new { ap = tagreads.antennaPort, rd = readerdata.Id }
        equals new { ap = locations.AntennaId, rd = locations.ReaderId }
    group tags by new { tags.TagFriendlyName, timestamp = tagreads.timeStamp, readerdata.mac_address } into grp

    select new CurrentStatus()
    {
        TagName = grp.Key.TagFriendlyName,
        LastSeen = grp.Key.timestamp,
        LocationName = grp.Key.mac_address
    }
)
.OrderByDescending(o => o.LastSeen)

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