I cant get the fallowing request working in Mono:
Without joins it would work.
when I only select t1 it also works, but I cant select something from both tables.
I think I want a left join, where I always have entries in t1 and IF the NameOfFile matches FileName then I want to have the tables joined.
Extra Question: When is my query executed? When I run the foreach loop?
var result = (
from t1 in db.Table1
join t2 in db.Table2 on t1.FileName equals t2.NameOfFile
into joinDep
from t3 in joinDep.DefaultIfEmpty ()
select new
{
Time = t1.WriteTime,
Name = t2.NameOfFile
}
)
.OrderByDescending (c => c.Time.Date)
.Take (10);
foreach (var entry in result)
{
Console.WriteLine (entry.Name );
}
Use this:
var query = from t1 in db.Table1
join t2 in db.Table2 on t1.FileName equals t2.NameOfFile into gj
from joinDep in gj.DefaultIfEmpty ()
select new
{
Time = t1.WriteTime,
Name = joinDep.NameOfFile
};
var result = query.OrderByDescending (c => c.Time.Date)
.Take (10);
Yes. Take uses deferred execution.
Related
I am new to Linq. I am trying to query some data in MS SQL.
Here is my statement:
select * from booking
left outer join carpark
on booking.bookingId = carpark.bookingId
where userID = 5 and status = 'CL'
When I run this in MS SQL, I get the expected result. How can I do this in Linq?
Thank you for your help.
you need this:
var query = (from t1 in tb1
join t2 in tb2 on t1.pKey = t2.tb1pKey into JoinedList
from t2 in JoinedList.DefaultIfEmpty()
where t1.userID == 5 && t1.status == "CL"
select new
{
t1,
t2
})
.ToList();
You can try to do left join this way :
from t1 in tb1
from t2 in tb2.Where(o => o.tb1pKey == t1.pKey).DefaultIfEmpty()
where tb1.userId == 5 && tb1.status == "CL"
select t1;
Usually when people say they want a "left outer join," that's just because they've already converted what they really want into SQL in their head. Usually what they really want is all of the items from table A, and the ability to get the related items from table B if there are any.
Assuming you have your navigation properties set up correctly, this could be as easy as:
var tb1sWithTb2s = context.tb1
.Include(t => t.tb2s) // Include all the tb2 items for each of these.
.Where(t => t.userID == 5 and t.status = "CL");
I want to join the following Tables
1. B_Book[1st Table]
-B_BID (Book ID)(PK)
-B_Name
-B_CategroyID (FK)
2. BI_BookInstance [2nd Table]
-BI_IID(Instance ID)
-BI_BID (FK)
-BI_Price
3. BC_BookCategory [3rd Table]
-BC_CategoryID (PK)
-BC_CategoryName
First Join B_Book and BI_BookInstance then join the result of those both with BookCategory.
(1st join)[B_BID equals BI_BID]
(2nd nested join)[result of 1st join B_CategoryID equals BC_CategoryID]
Edit
SQL would be something like the following:
SELECT * FROM
(SELECT * FROM B_Book b JOIN BI_BookInstance bi on b.B_BID = bi.BI_BID) as t1
JOIN BC_BookCategoryID bc on bc.BC_CategoryID = t1.B_CategoryID
What matches your query in LINQ would be the following (and you'll notice the similarity with SQL). I've also included some examples on how to rename the fields returned, such as Price or CategoryName:
var results = from b in B_Book
join bi in BI_BookInstance
on b.B_BID equals bi.BI_BID
join bc in BC_BookCategory
on b.B_CategoryID equals bc.BC_CategoryID
select new
{
// put in whatever fields you want returned here:
b.B_BID,
b.B_CategoryID,
b.B_Name,
bi.BI_BID,
bi.BI_IID,
Price = bi.BI_Price,
bc.BC_CategoryID,
CategoryName = bc.BC_CategoryName
};
I have supposed inner joins (your FKs is not null), so i would like query like this:
var ctx = new YourEntities();
var query = from b in ctx.B_Book
from bi in ctx.BI_BookInstance
from bc in ctx.BC_BookCategory
where b.B_BID == bi.BI_BID && b.B_CategoryID == bc.BC_CategoryID
select new
{
BInstID = bi.BI_IID,
BName = b.B_Name,
BPrice = bi.BI_Price,
BCategory = bc.BC_CategoryName
};
foreach (var item in query)
{
Console.WriteLine(item.BInstID);
Console.WriteLine(item.BName);
Console.WriteLine(item.BPrice);
Console.WriteLine(item.BCategory);
Console.WriteLine("");
}
You can do this without explicitly using linq's join statement, provided that navigation properties are in place:
from b in ctx.B_Book
from bi in b.BookInstances
select new { b.Property1, bi.Property2, b.BookCategory.Name }
I need to write Join statment after writing query in linq
example :
var Query = (from Tab in Db.Employees
select Tab)
as i have some cases to perform join operation so
i need to do it on this Query Query.Join(Join with another Table like Department); I need the Syntax
if (DeptID != -1){ Query.Join(Join with table Department where FkDeptID = DeptID); }
Consider the usage of join in the LINQ 'query syntax':
from t1 in db.Table1
join t2 in db.Table2 on t1.field equals t2.field
select new { t1.field2, t2.field3}
Something like this?
var results = (from q in Query
join m in myList on q.SomeID = m.SomeID
select unknown);
Try using this query:
var Query =
from e in Db.Employees
join d in Db.Departments on e.FkDeptID equals d.DeptID into departments
select new
{
Employee = e,
Department = departments.SingleOrDefault(),
};
This works assuming that when e.FkDeptID == -1 that there is no record in the Departments table and in that case Department would be assigned null.
You should never have more than one department for an employee so I've used SingleOrDefault rather than FirstOrDefault.
I have a query that has the following
var myvar = from table in MyDataModel
where.....
select new MyModel
{
modelvar1 = ...,
modelvar2 = (from..... into anothervar)
}
What I want to do is have modelvar2 be a join between the result I currently get from anothervar with another table in MyDataModel.
Thanks
The parenthesis looks more like a subquery than a join. This is how you do a join.
Example tables from the AdventureWorks database.
using (DataClasses1DataContext context = new DataClasses1DataContext())
{
// If you have foreign keys correctly in your database you can
// join implicitly with the "dot" notation.
var myvar = from prod in context.Products
where prod.ListPrice < 10
select new
{
Name = prod.Name,
Category = prod.ProductSubcategory.ProductCategory.Name,
};
// If you don't have foreign keys you need to express the join
// explicitly like this
var myvar2 = from prod in context.Products
join prodSubCategory in context.ProductSubcategories
on prod.ProductSubcategoryID equals prodSubCategory.ProductSubcategoryID
join prodCategory in context.ProductCategories
on prodSubCategory.ProductCategoryID equals prodCategory.ProductCategoryID
where prod.ListPrice < 10
select new
{
Name = prod.Name,
Category = prodCategory.Name,
};
// If you REALLY want to do a subquery, this is how to do that
var myvar3 = from prod in context.Products
where prod.ListPrice < 10
select new
{
Name = prod.Name,
Category = (from prodSubCategory in context.ProductSubcategories
join prodCategory in context.ProductCategories
on prodSubCategory.ProductCategoryID equals prodCategory.ProductCategoryID
select prodCategory.Name).First(),
};
// If you want to get a list from the subquery you can do like this
var myvar4 = from prodCategory in context.ProductCategories
select new
{
Name = prodCategory.Name,
Subcategoreis = (from prodSubCategory in context.ProductSubcategories
where prodSubCategory.ProductCategoryID == prodCategory.ProductCategoryID
select new { prodSubCategory.ProductSubcategoryID, prodSubCategory.Name }).ToList(),
};
}
SELECT [t0].[OrderID], [t0].[CustomerID], [t0].[EmployeeID], [t0].[OrderDate], [t0].[RequiredDate], [t0].[ShippedDate], [t0].[ShipVia], [t0].[Freight], [t0].[ShipName], [t0].[ShipAddress], [t0].[ShipCity], [t0].[ShipRegion], [t0].[ShipPostalCode], [t0].[ShipCountry]
FROM [Orders] AS [t0]
INNER JOIN ([Order Details] AS [t1]
INNER JOIN [Products] AS [t2] ON [t1].[ProductID] = [t2].[ProductID]) ON [t0].[OrderID] = [t1].[OrderID]
can be write as
from o in Orders
join od in (
from od in OrderDetails join p in Products on od.ProductID equals p.ProductID select od)
on o.OrderID equals od.OrderID
select o
This is the SQL I want (ClearinghouseKey is a bigint):
select *
from ConsOutput O
where O.ClearinghouseKey IN (
select distinct P.clearinghouseKey
from Project P
Inner join LandUseInProject L on L.ClearinghouseKey = P.ClearinghouseKey
where P.ProjectLocationKey IN ('L101', 'L102', 'L103')
and L.LandUseKey IN ('U000', 'U001', 'U002', 'U003')
)
The inner query is straight forward and gives correct results in LINQPad:
var innerQuery = (from p in Projects
join l in LandUseInProjects on p.ClearinghouseKey equals l.ClearinghouseKey
where locations.Contains(p.ProjectLocationKey)
&& (landuses.Contains(l.LandUseKey))
select new { p.ClearinghouseKey }).Distinct();
But the outer query gives the error: Type arguments from ...Contains..cannot be inferred from usage:
var returnQuery = from o in OperOutput
where (innerQuery).Contains(o.ClearinghouseKey)
select o;
Is it because ClearinghouseKey is a bigint? Any other ways to write this query?
Thanks,
Jeanne
Don't use an anonymous type:
select new { p.ClearinghouseKey })
Should be
select p.ClearinghouseKey)
Also consider using Any instead of Contains (I don't have reasons for choosing one over the other, yet).
where innerQuery.Any(i => i == o.ClearinghouseKey)