We Keep Coding

Entity Framework (using In and Select Distinct)

I am relatively new to Entity Framework 6.0 and I have come across a situation where I want to execute a query in my C# app that would be similar to this SQL Query:
select * from periods where id in (select distinct periodid from ratedetails where rateid = 3)
Is it actually possible to execute a query like this in EF or would I need to break it into smaller steps?

Assuming that you have in your Context class:
DbSet<Period> Periods...
DbSet<RateDetail> RateDetails...
You could use some Linq like this:
var distincts = dbContext.RateDetails
.Where(i => i.rateId == 3)
.Select(i => i.PeriodId)
.Distinct();
var result = dbContext.Periods
.Where(i => i.Id)
.Any(j => distincts.Contains(j.Id));
Edit: Depending on your entities, you will probably need a custom Comparer for Distinct(). You can find a tutorial here, and also here
or use some more Linq magic to split the results.

Yes, this can be done but you should really provide a better example for your query. You are already providing a bad starting point there. Lets use this one:
SELECT value1, value2, commonValue
FROM table1
WHERE EXISTS (
SELECT 1
FROM table2
WHERE table1.commonValue = table2.commonValue
// include some more filters here on table2
)
First, its almost always better to use EXISTS instead of IN.
Now to turn this into a Lambda would be something like this, again you provided no objects or object graph so I will just make something up.
DbContext myContext = this.getContext();
var myResults = myContext.DbSet<Type1>().Where(x => myContext.DbSet<Type2>().Any(y => y.commonValue == x.commonValue)).Select(x => x);
EDIT - updated after you provided the new sql statement
Using your example objects this would produce the best result. Again, this is more efficient than a Contains which translates to an IN clause.
Sql you really want:
SELECT *
FROM periods
WHERE EXISTS (SELECT 1 FROM ratedetails WHERE rateid = 3 AND periods.id = ratedetails.periodid)
The Lamda statement you are after
DbContext myContext = this.getContext();
var myResults = myContext.DbSet<Periods>()
.Where(x => myContext.DbSet<RateDetails>().Any(y => y.periodid == x.id && y.rateid == 3))
.Select(x => x);
Here is a good starting point for learning about lamda's and how to use them.
Lambda Expressions (C# Programming Guide).

this is your second where clause in your query
var priodidList=ratedetails.where(x=>x.rateid ==3).DistinctBy(x=>x.rateid);
now for first part of query
var selected = periods.Where(p => p.id
.Any(a => priodidList.Contains(a.periodid ))
.ToList();

Linq To SQL Contains

How can I go about converting this SQL statement to LINQ:
SELECT [Content].[Content], [Content].ListOrder, [Content].ContentTypeId,
[Content].ContentId
FROM [Content] INNER JOIN
GroupContentPermission ON [Content].ContentId = GroupContentPermission.ContentId
WHERE GroupContentPermission.GroupId IN
(SELECT GroupId FROM GroupUser WHERE GroupUser.UserId = 169)

Translation to LINQ is generally pretty straightforward except for one special trick in the case of your query. You can translate your select, where, and from statements in a natural way as shown below. In the case of an IN statement though, you have to get the results from the inner subquery first, and then check if the inner subquery .Contains the value you want to check.
var groups =
(from gu in GroupUser
where gu.UserId == 169
select gu.GroupId).ToList();
var result =
from p in GroupContentPermission
join c in Content on p.ContentId equals c.ContentId
where groups.Contains(p.GroupId)
select new { c.Content, c.ListOrder, c.ContentTypeID, c.ContentId };
// result should contain the same results as the SQL query
Here are some other resources you may find helpful as well (you can find many more resources and tutorials on LINQ if you do a quick google search. There are literally thousands):
Linqer, a SQL to LINQ converter.
LinqPAD, a simple .NET/LINQ tester for rapid experimentation
ScottGu's definitive guide to Using LINQ To SQL
Related SO question: What are some good LINQ resources?, which references a tutorial called 101 LINQ Samples.

Assuming you already link the tables with foreign keys in your model (DBML/EntityFrameworks):
Contents.Where(x => x.GroupContentPermission.GroupUser.UserId == 169).Select(x => new {
x.Content,
x.ListOrder,
x.ContentTypeId,
x.ContentId })
or preferrably just grab the full Content object, and use any column you want:
var contents = Contents.Where(x => x.GroupContentPermission.GroupUser.UserId == 169).ToList();
foreach (var content in contents)
Console.Write(content.Content);

Using the equivalent to the SQL IN function with LINQ with a collection

How do I translate the following in LINQ?
SELECT DISTINCT w.Worker_ID, w.Surname, w.FirstName, ps.JobNumber
FROM Worker w, ProjectSignatory ps
where w.Worker_ID = ps.Worker_ID
and ps.JobNumber
IN
(SELECT DISTINCT pa.JobNumber
FROM Worker w, PAAFRegister pa
where w.Worker_ID = pa.Worker_ID
and w.Worker_ID = #UserX)
I have seen anumber of posts which sugges that the .Contains function is a good idea, however since I am looking through a collection of results then based from what I have seen on other responses LINQ does not like it when people call .Contains on a collection.
I am trying to understand the workings of LINQ on the whole. I am relatively inexperienced. Any advice would be greatly appreciated.
EDIT: I have seen a few approaches and I am wondering if the following is a good start or would it be best achieved using a linge query using joins?
var sig = from w in db.Workers
join ps in db.ProjectSignatories
on w.Worker_ID equals ps.Worker_ID
select ps;
var paaf = from w in db.Workers
join pa in db.PAAFRegisters
on w.Worker_ID equals pa.Worker_ID
where w.Worker_ID == workerID
select w;
I am aware that this is incomplete and seves no purpose or makes no sense to what I am attempting to achieve. This was merely an example based on previous posts I have seen and wondering if the approach is suitable.
Thanks!

You're looking for the .Contains() function.
First build up the inner filter set section of the query.
E.G.: The part that goes in the .Contains() (in SQL terms the "ps.JobNumber IN (...)" )
Filter your query by the new data subset by using the .Contains function.
Example:
C# SQL-like syntax:
var subSet = select JobNumber
from Workers
where Worker_ID == "UserX";
var result = select JobNumber
from Workers
where subSet.Contains(jobnumber);
LINQ chaining:
var subSet = Workers.Where(o => o.Worker_ID == "UserX")
.Select(o => o.JobNumber)
.Distinct();
var result = Workers.Where(o => subSet.Contains(o.JobNumber)).ToList();

You can create subselect's in LINQ.
var jobNumbers = select JobNumber from Workers where <your criteria, joins>
var myResult = select JobNumber from Workers where <your criteria, joins> and jobNumbers.Contains(JobNumber)

How can i add a condition string to an sql query in an var type

Im working on an source code with an sql query in a VAR type like
var query = select ... from ... where ... ;
is it possible to add an dynamic "where clause" like
string condition = "where x.x > x.y";
e.g. var query = select ... from ... + condition;
Iam sorry for my bad english

You are not clearly stating how your query looks like. Is it a result of a LINQ operation or simply a String?
The keyword var is only usable for design time. The compiler will substitute it with the correct datatype.
If you SQL query is a string, like
var query = "Select ... from ... where ..";
then
string condition = "where x.x > x.y";
query += condition;
is valid because both variables are strings. You can't combine a non string type with a string the way your code suggests.
I do now assume that you are using a LINQ syntax. It is possible to add such conditions to a linq query per code, I think the keywords linq query builder, expression tree and predicate should get you started.
I'd strongly suggest that you stop using the var keyword without exactly knowing what it does and where to use it.

Dynamic Linq exists specifically to solve late-bound scenarios for LINQ:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
Allows constructs such as:
NorthwindDataContext northwind = new NorthwindDataContext();
var query = northwind.Products
.Where("CategoryID = 3 AND UnitPrice > 3")
.OrderBy("SupplierID");

If you do not call ToList() and your final mapping to the DTO type, you can add Where clauses as you go, and build the results at the end:
var query = from u in DataContext.Users
where u.Division == strUserDiv
&& u.Age > 18
&& u.Height > strHeightinFeet
select u;
if (useAge)
query = query.Where(u => u.Age > age);
if (useHeight)
query = query.Where(u => u.Height > strHeightinFeet);
// Build the results at the end
var results = query.Select(u => new DTO_UserMaster
{
Prop1 = u.Name,
}).ToList();
This will still only result in a single call to the database, which will be effectively just as efficient as writing the query in one pass.
I saw this answer here by Reed Copsey

Which ORM Supports this

I have an optional part of query that needs to be executed on a certain condition. Here is the example code:
int cat = 1;
int UserID = 12;
string qry = "select * from articles";
if(cat > 0)
qry += " where categoryID = " + cat;
if(UserID > 0)
qry += " AND userid = " + UserID; //The AND may be a WHERE if first condition is false
As you can see I have an if statement in the query. i am currently using Entity Framework and it does not support this kind of scenario. Is there an ORM out there that support this?
Edit
I tried to dummy down the query. But I have about 20 "IF" statements and the querys are very long.
The ORMs I was looking at were:
NHibernate
LLBLGen
Subsonic
I am open to any ORM. Thanks

As it was already mentioned here, LINQ allows to extend any query by simply adding more criteria to it.
var query =
from x in xs
where x==1
select x;
if (mustAddCriteria1)
query =
from x in query
where ... // criteria 1
select x;
if (mustAddCriteria2)
query =
from x in query
where ... // criteria 2
select x;
And so on. This approach works just perfectly. But likely, you know that compilation of LINQ queries is pretty expensive: e.g. Entity Framework can compile just about 500 relatively simple queries per second (see e.g. ORMBattle.NET).
On the other hand, many ORM tools support compiled queries:
You pass an IQueryable instance to some Compile method, and get a delegate allowing to execute it much faster later, because no recompilation would occur in this case.
But if we'd try to use this approach here, we immediately notice that our query is actually dynamic: IQueryable we execute each time might differ from the previous one. Presence of query parts there is determined by values of external parameters.
So can we execute such queries as compiled without e.g. explicit caching?
DataObjects.Net 4 support so-called "boolean branching" feature. It implies any constant boolean expression is evaluated during query compilation and its actual value is injected into SQL query as true boolean constant (i.e. not as parameter value or as an expression utilizing parameters).
This feature allows to generate different query plans dependently on values of such boolean expressions with ease. E.g. this code:
int all = new Random().Next(2);
var query =
from c in Query<Customer>.All
where all!=0 || c.Id=="ALFKI"
select c;
will be executed using two different SQL queries, and thus - two different query plans:
Query plan based on index seek (quite fast), if all==0
Query plan based on index scan (quite slow), if all!=0
Case when all==null, SQL query:
SELECT
[a].[CustomerId],
111 AS [TypeId] ,
[a].[CompanyName]
FROM
[dbo].[Customers] [a]
WHERE(( CAST( 0 AS bit ) <> 0 ) OR( [a].[CustomerId] = 'ALFKI' ) );
Case when all==null, query plan:
|--Compute Scalar(DEFINE:([Expr1002]=(111)))
|--Clustered Index Seek(OBJECT:([DO40-Tests].[dbo].[Customers].[PK_Customer] AS [a]), SEEK:([a].[CustomerId]=N'ALFKI') ORDERED FORWARD)
Second case (when all!=null), SQL query:
SELECT
[a].[CustomerId],
111 AS [TypeId] ,
[a].[CompanyName]
FROM
[dbo].[Customers] [a]
WHERE(( CAST( 1 AS bit ) <> 0 ) OR( [a].[CustomerId] = 'ALFKI' ) );
-- Notice the ^ value is changed!
Second case (when all!=null), query plan:
|--Compute Scalar(DEFINE:([Expr1002]=(111)))
|--Clustered Index Scan(OBJECT:([DO40-Tests].[dbo].[Customers].[PK_Customer] AS [a]))
-- There is index scan instead of index seek!
Note that almost any other ORM would compile this to a query utilizing integer parameter:
SELECT
[a].[CustomerId],
111 AS [TypeId] ,
[a].[CompanyName]
FROM
[dbo].[Customers] [a]
WHERE(( #p <> 0 ) OR ( [a].[CustomerId] = 'ALFKI' ) );
-- ^^ parameter is used here
Since SQL Server (as well as most of databases) generates a single version of query plan for a particular query, it has the only option in this case - generate a plan with index scan:
|--Compute Scalar(DEFINE:([Expr1002]=(111)))
|--Clustered Index Scan(OBJECT:([DO40-Tests].[dbo].[Customers].[PK_Customer] AS [a]), WHERE:(CONVERT(bit,[#p],0)<>(0) OR [DO40-Tests].[dbo].[Customers].[CustomerId] as [a].[CustomerId]=N'ALFKI'))
Ok, that was a "quick" explanation of usefulness of this feature. Let's return back to your case now.
Boolean branching allows to implement it in very simple fashion:
var categoryId = 1;
var userId = 1;
var query =
from product in Query<Product>.All
let skipCategoryCriteria = !(categoryId > 0)
let skipUserCriteria = !(userId > 0)
where skipCategoryCriteria ? true : product.Category.Id==categoryId
where skipUserCriteria ? true :
(
from order in Query<Order>.All
from detail in order.OrderDetails
where detail.Product==product
select true
).Any()
select product;
The example differs from yours, but it illustrates the idea. I used different model mainly to be able to test this (my example is based om Northwind model).
This query is:
Not a dynamic query, so you can safely pass it to Query.Execute(...) method to get it executed as compiled query.
Nevertheless each its execution will lead to the same result as if this would be done with "appending" to IQueryable.

this can be done using linq to sql...
IQueryable<Article> query = yourDataContext.Articles;
if (catId > 0)
query = query.Where(x => x.CategoryId == catId);
return query.ToList();

NHibernate supports this using the Criteria API:
ICriteria criteria = session.CreateCriteria<Article>();
if (cat > 0)
criteria.Add(Expression.Eq("categoryID", cat));

You can probably do this with any LINQ provider, but I know the LightSpeed ORM supports it:
var query = UnitOfWork.Articles;
if (cat > 0)
query = query.Where(a => a.CategoryId == cat);

I do this kind of thing in NHibernate all the time.
(I've done similar things in Rails. I'm kind of surprised that there are ORMs that don't support this.)

You can easily build queries in this way using NHibernate's HQL (Hibernate Query Language). It would be an almost identical implementation but I would personally use parameters.
public List<Article> GetCat(int cat)
{
string qry = "select ap from Article a";
if(cat > 0)
qry += " where a.categoryID = :cat";
IQuery query = session.CreateQuery(qry).SetInt32("cat",cat);
return query.List<Article>();
}
This returns a List<> of Article objects ready for use.

No love for LLBLGen? Well it can can do it too.
Using the 'adapter' style:
RelationPredicateBucket filters = new RelationPredicateBucket();
if (cat > 0)
filters.Predicate.Add(Article.Fields.CategoryID == cat);
if (userId > 0)
filters.Predicate.Add(Article.Fields.UserID == userId);
// And so on.
var adapter = new DataAccessAdapter();
var results = new EntityCollection<Article>(new ArticleFactory());
adapter.FetchEntityCollection(results, filters);
I would suspect most ORMs should be able to do this pretty easily.

You can use the Predicate Builder and LINQ to NHibernate to generate dynamic query's like this:
//using Predicate Builder
public List<Location> FindAllMatching(string[] filters)
{
var db = Session.Linq<Location>();
var expr = PredicateBuilder.False<Location>(); //-OR-
foreach (var filter in filters)
{
string temp = filter;
expr = expr.Or(p => p.Name.Contains(temp));
}
return db.Where(expr).ToList();
}
You get the advantage of Type Save Query's and Compiler check.
You can also use the same approach of predicate builder with Linq to Sql and Entity Framework.
EDIT: Added example.
It could be something like get all the locations matching N regions of the world, where the user select the regions he want to see, we don't know how many the user will select, we must build the (OR) expression on the fly, you can do something like:
public ActionResult Action(string[] filters)
{
/*This values are provided by the user, maybe its better to use
an ID instead of the name, but for the example is OK.
filters will be something like : string[] filters = {"America", "Europe", "Africa"};
*/
List<Location> LocationList = FindAllMatchingRegions(filters);
return View(LocationList);
}
public List<Location> FindAllMatchingRegions(string[] filters)
{
var db = Session.Linq<Location>();
var expr = PredicateBuilder.False<Location>(); //-OR-
foreach (var filter in filters)
{
string temp = filter;
expr = expr.Or(p => p.Region.Name == filter);
}
return db.Where(expr).ToList();
}
You can Nest Predicates for a complex scenarios like this:
If you want to do something like
p => p.Price > 99 &&
p.Price < 999 &&
(p.Description.Contains ("foo") || p.Description.Contains ("far"))
you can build:
var inner = PredicateBuilder.False<Product>();
inner = inner.Or (p => p.Description.Contains ("foo"));
inner = inner.Or (p => p.Description.Contains ("far"));
var outer = PredicateBuilder.True<Product>();
outer = outer.And (p => p.Price > 99);
outer = outer.And (p => p.Price < 999);
outer = outer.And (inner);
And use it like :
var pr = db.Products.Where(outer).ToList();
The Predicate Builder Source and examples are available at http://www.albahari.com/nutshell/predicatebuilder.aspx