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LLBLGen load a distinct item by fields that are not primary key

I have been trying to load single items from with LLBLGen by fields in the table that are not primary keys.
I can only work out how to filer on primary keys on FetchEntity.
To filter on non primary keys I am having to getthe collection and use linq to get the first.
It fells like a smell, I was wondering if there was a better way?
public BinLocationEntity GetDefaultBinLocation(string firstName, string lastName)
{
var persons = new EntityCollection<PersonEntity>();
var filter = new RelationPredicateBucket();
filter.PredicateExpression.Add(PersonFields.FirstName == firstName);
filter.PredicateExpression.Add(PersonFields.LastName== lastName);
using (var adapter = this.DataAccessAdapter)
{
adapter.FetchEntityCollection(persons , filter);
}
return persons .First();
}
I know the demo code would be bad in real world, Its just there as an example.

You can also fetch by unique constraint:
https://www.llblgen.com/Documentation/5.6/LLBLGen%20Pro%20RTF/Using%20the%20generated%20code/Adapter/gencode_usingentityclasses_instantiating.htm#using-a-unique-constraints-value
It does not make a lot of sense to (directly) fetch a single entity using fields that are not primary keys and are not unique constraints. The generated code has no way to know that your query should logically result in a single entity being returned.
Using Linq .First() in these cases is completely appropriate and not at all a code/design smell.

The only thing that i'd add to your answer is that if you truly do expect that your query is going to return just a single result, that you change your FetchEntityCollection() call to:
adapter.FetchEntityCollection(persons , filter, 1);
to specifically limit the results to 0 or 1 rows. It might well be that the first result is the one you want, but without any top limit supplied it could be that this query is returning thousands of rows or more which can incur a huge performance hit.

get related data from ms dynamics crm using XRM SDK

I'm trying to retrieve data from crm in a .net application, using the SDK.
I've managed to do simple queries to retrieve lists, but I would now like to get the related entities with items, rather than the ids.
I have tried things like
QueryExpression query = new QueryExpression
{
EntityName = "opportunity",
....
LinkEntity linkEntityAccount = new LinkEntity()
{
LinkFromEntityName = "opportunity",
LinkFromAttributeName = "opportunityid",
LinkToEntityName = "serviceappointment",
LinkToAttributeName = "regardingobjectid",
JoinOperator = JoinOperator.Inner,
Columns = new ColumnSet(new string[] { "scheduledstart", "scheduledend" }),
EntityAlias = "service"
};
query.LinkEntities.Add(linkEntityAccount);
(This will return a collection of entities from the opportunity table)
However the LinkedEntities just put the two columns in the returns entities.
What i would like is (say for this example) is a entity.serviceappointment to be the the entity containing the service appointment entity/data. Instead of in entity there being fields such as service.scheduledstart and service.scheduledend
I have looked at the Relationship and RelationshipQueryCollection things in the SDK but i have been unable to setup a query that will do the query, without first getting the opportunity entities. But it looks like that maybe what I need? I'm not sure.
Is this even possible? Or should I just continue to query entities individually?
Thanks

In the QueryExpression the LinkEntity represents a join. That's why the fields of the joined table are in the Entity row. They can be distinguished from the 'real' entity attributes by the fact that their names are prefixed (including a dot) and their values are wrapped in an AliasedValue object.
It is possible to unwrap them and create strong typed Entity objects, but you will need to write the code yourself.
Alternatively you can consider a few other options:
Query for serviceappointment records and join the opportunity records.
Retrieve opportunity records one by one using the RetrieveRequest and include the query for the related service appointments in the request. (See also this discussion on StackOverflow.)
Create an Action returning all data you need in a convenient OrganizationResponse.

There's no automatic way to get the entire linked entity data (as an Entity object) that I know of (that's not to say it's impossible, mind you).
But I think it'd be a lot easier to just query the data you need in another request.
Find the list of opportunities you need
Use the regarding object IDs as the parameter of an "IN" filter for the second query.

How do I apply the LINQ to SQL Distinct() operator to a List<T>?

I have a serious(it's getting me crazy) problem with LINQ to SQL. I am developing an ASP.NET MVC3 application using c# and Razor in Visual Studio 2010.
I have two database tables, Product and Categories:
Product(Prod_Id[primary key], other attributes)
Categories((Dept_Id, Prod_Id) [primary keys], other attributes)
Obviously Prod_Id in Categories is a foreign key. Both classes are mapped using the Entity Framework (EF). I do not mention the context of the application for simplicity.
In Categories there are multiple rows containing the Prod_Id. I want to make a projection of all Distinct Prod_Id in Categories. I did it using plain (T)SQL in SQL Server MGMT Studio according to this (really simple) query:
SELECT DISTINCT Prod_Id
FROM Categories
and the result is correct. Now I need to make this query in my application so I used:
var query = _StoreDB.Categories.Select(m => m.Prod_Id).Distinct();
I go to check the result of my query by using:
query.Select(m => m.Prod_Id);
or
foreach(var item in query)
{
item.Prod_Id;
//other instructions
}
and it does not work. First of all the Intellisense when I attempt to write query.Select(m => m. or item.shows just suggestions about methods (such as Equals, etc...) and not properties. I thought that maybe there was something wrong with Intellisense (I guess most of you many times hoped that Intellisense was wrong :-D) but when I launch the application I receive an error at runtime.
Before giving your answer keep in mind that;
I checked many forums, I tried the normal LINQ to SQL (without using lambdas) but it does not work. The fact that it works in (T)SQL means that there is something wrong with the LINQ to SQL instruction (other queries in my application work perfectly).
For application related reasons, I used a List<T> variable instead of _StoreDB.Categories and I thought that was the problem. If you can offer me a solution without using a List<T> is appreciated as well.

This line:
var query = _StoreDB.Categories.Select(m => m.Prod_Id).Distinct();
Your LINQ query most likely returns IEnumerable... of ints (judging by Select(m => m.Prod_Id)). You have list of integers, not list of entity objects. Try to print them and see what you got.

Calling _StoreDB.Categories.Select(m => m.Prod_Id) means that query will contain Prod_Id values only, not the entire entity. It would be roughly equivalent to this SQL, which selects only one column (instead of the entire row):
SELECT Prod_Id FROM Categories;
So when you iterate through query using foreach (var item in query), the type of item is probably int (or whatever your Prod_Id column is), not your entity. That's why Intellisense doesn't show the entity properties that you expect when you type "item."...
If you want all of the columns in Categories to be included in query, you don't even need to use .Select(m => m). You can just do this:
var query = _StoreDB.Categories.Distinct();
Note that if you don't explicitly pass an IEqualityComparer<T> to Distinct(), EqualityComparer<T>.Default will be used (which may or may not behave the way you want it to, depending on the type of T, whether or not it implements System.IEquatable<T>, etc.).
For more info on getting Distinct to work in situations similar to yours, take a look at this question or this question and the related discussions.

As has been explained by the other answers, the error that the OP ran into was because the result of his code was a collection of ints, not a collection of Categories.
What hasn't been answered was his question about how to use the collection of ints in a join or something in order to get at some useful data. I will attempt to do that here.
Now, I'm not really sure why the OP wanted to get a distinct list of Prod_Ids from Categories, rather than just getting the Prod_Ids from Projects. Perhaps he wanted to find out what Products are related to one or more Categories, thus any uncategorized Products would be excluded from the results. I'll assume this is the case and that the desired result is a collection of distinct Products that have associated Categories. I'll first answer the question about what to do with the Prod_Ids first, and then offer some alternatives.
We can take the collection of Prod_Ids exactly as they were created in the question as a query:
var query = _StoreDB.Categories.Select(m => m.Prod_Id).Distinct();
Then we would use join, like so:
var products = query.Join(_StoreDB.Products, id => id, p => p.Prod_Id,
(id,p) => p);
This takes the query, joins it with the Products table, specifies the keys to use, and finally says to return the Product entity from each matching set. Because we know that the Prod_Ids in query are unique (because of Distinct()) and the Prod_Ids in Products are unique (by definition because it is the primary key), we know that the results will be unique without having to call Distinct().
Now, the above will get the desired results, but it's definitely not the cleanest or simplest way to do it. If the Category entities are defined with a relational property that returns the related record from Products (which would likely be called Product), the simplest way to do what we're trying to do would be the following:
var products = _StoreDB.Categories.Select(c => c.Product).Distinct();
This gets the Product from each Category and returns a distinct collection of them.
If the Category entity doesn't have the Product relational property, then we can go back to using the Join function to get our Products.
var products = _StoreDB.Categories.Join(_StoreDB.Products, c => c.Prod_Id,
p => p.Prod_Id, (c,p) => p).Distinct();
Finally, if we aren't just wanting a simple collection of Products, then some more though would have to go into this and perhaps the simplest thing would be to handle that when iterating through the Products. Another example would be for getting a count for the number of Categories each Product belongs to. If that's the case, I would reverse the logic and start with Products, like so:
var productsWithCount = _StoreDB.Products.Select(p => new { Product = p,
NumberOfCategories = _StoreDB.Categories.Count(c => c.Prod_Id == p.Prod_Id)});
This would result in a collection of anonymous typed objects that reference the Product and the NumberOfCategories related to that Product. If we still needed to exclude any uncatorized Products, we could append .Where(r => r.NumberOfCategories > 0) before the semicolon. Of course, if the Product entity is defined with a relational property for the related Categories, you wouldn't need this because you could just take any Product and do the following:
int NumberOfCategories = product.Categories.Count();
Anyway, sorry for rambling on. I hope this proves helpful to anyone else that runs into a similar issue. ;)

Linq is returning too many results when joined

In my schema I have two database tables. relationships and relationship_memberships. I am attempting to retrieve all the entries from the relationship table that have a specific member in it, thus having to join it with the relationship_memberships table. I have the following method in my business object:
public IList<DBMappings.relationships> GetRelationshipsByObjectId(int objId)
{
var results = from r in _context.Repository<DBMappings.relationships>()
join m in _context.Repository<DBMappings.relationship_memberships>()
on r.rel_id equals m.rel_id
where m.obj_id == objId
select r;
return results.ToList<DBMappings.relationships>();
}
_Context is my generic repository using code based on the code outlined here.
The problem is I have 3 records in the relationships table, and 3 records in the memberships table, each membership tied to a different relationship. 2 membership records have an obj_id value of 2 and the other is 3. I am trying to retrieve a list of all relationships related to object #2.
When this linq runs, _context.Repository<DBMappings.relationships>() returns the correct 3 records and _context.Repository<DBMappings.relationship_memberships>() returns 3 records. However, when the results.ToList() executes, the resulting list has 2 issues:
1) The resulting list contains 6 records, all of type DBMappings.relationships(). Upon further inspection there are 2 for each real relationship record, both are an exact copy of each other.
2) All relationships are returned, even if m.obj_id == 3, even though objId variable is correctly passed in as 2.
Can anyone see what's going on because I've spent 2 days looking at this code and I am unable to understand what is wrong. I have joins in other linq queries that seem to be working great, and my unit tests show that they are still working, so I must be doing something wrong with this. It seems like I need an extra pair of eyes on this one :)
Edit: Ok so it seems like the whole issue was the way I designed my unit test, since the unit test didn't actually assign ID values to the records since it wasn't hitting sql (for unit testing).
Marking the answer below as the answer though as I like the way he joins it all together better.

Just try like this
public IList<DBMappings.relationships> GetRelationshipsByObjectId(int objId)
{
var results = (from m in _context.Repository<DBMappings.relationship_memberships>()
where m.rel_id==objID
select m.relationships).ToList();
return results.ToList<DBMappings.relationships>();
}

How about to set _context.Log = Console.Out just to see the generated SQL query? Share the output with us (maybe use some streamwriter instead of console.out so that you can copy that easily and without mistakes).
Pz, the TaskConnect developer

I might have this backwards, but I don't think you need a join here. If you've setup your foreign keys correctly, this should work, right?
public IList<DBMappings.relationships> GetRelationshipsByObjectId(int objId)
{
var mems = _context.Repository<DBMappings.relationship_memberships>();
var results = mems.Where(m => m.obj_id == objId).Select(m => m.relationships);
return results.ToList<DBMappings.relationships>();
}
Here's the alternative (if I've reversed the mapping in my brain):
public IList<DBMappings.relationships> GetRelationshipsByObjectId(int objId)
{
var mems = _context.Repository<DBMappings.relationship_memberships>();
var results = mems.Where(m => m.obj_id == objId).SelectMany(m => m.relationships);
return results.ToList<DBMappings.relationships>();
}
Let me know if I'm way off with this, and I can take another stab at it.

Select clause containing non-EF method calls

I'm having trouble building an Entity Framework LINQ query whose select clause contains method calls to non-EF objects.
The code below is part of an app used to transform data from one DBMS into a different schema on another DBMS. In the code below, Role is my custom class unrelated to the DBMS, and the other classes are all generated by Entity Framework from my DB schema:
// set up ObjectContext's for Old and new DB schemas
var New = new NewModel.NewEntities();
var Old = new OldModel.OldEntities();
// cache all Role names and IDs in the new-schema roles table into a dictionary
var newRoles = New.roles.ToDictionary(row => row.rolename, row => row.roleid);
// create a list or Role objects where Name is name in the old DB, while
// ID is the ID corresponding to that name in the new DB
var roles = from rl in Old.userrolelinks
join r in Old.roles on rl.RoleID equals r.RoleID
where rl.UserID == userId
select new Role { Name = r.RoleName, ID = newRoles[r.RoleName] };
var list = roles.ToList();
But calling ToList gives me this NotSupportedException:
LINQ to Entities does not recognize
the method 'Int32
get_Item(System.String)' method, and
this method cannot be translated into
a store expression
Sounds like LINQ-to-Entities is barfing on my call to pull the value out of the dictionary given the name as a key. I admittedly don't understand enough about EF to know why this is a problem.
I'm using devart's dotConnect for PostgreSQL entity framework provider, although I assume at this point that this is not a DBMS-specific issue.
I know I can make it work by splitting up my query into two queries, like this:
var roles = from rl in Old.userrolelinks
join r in Old.roles on rl.RoleID equals r.RoleID
where rl.UserID == userId
select r;
var roles2 = from r in roles.AsEnumerable()
select new Role { Name = r.RoleName, ID = newRoles[r.RoleName] };
var list = roles2.ToList();
But I was wondering if there was a more elegant and/or more efficient way to solve this problem, ideally without splitting it in two queries.
Anyway, my question is two parts:
First, can I transform this LINQ query into something that Entity Framework will accept, ideally without splitting into two pieces?
Second, I'd also love to understand a little about EF so I can understand why EF can't layer my custom .NET code on top of the DB access. My DBMS has no idea how to call a method on a Dictionary class, but why can't EF simply make those Dictionary method calls after it's already pulled data from the DB? Sure, if I wanted to compose multiple EF queries together and put custom .NET code in the middle, I'd expect that to fail, but in this case the .NET code is only at the end, so why is this a problem for EF? I assume the answer is something like "that feature didn't make it into EF 1.0" but I am looking for a bit more explanation about why this is hard enough to justify leaving it out of EF 1.0.

The problem is that in using Linq's delayed execution, you really have to decide where you want the processing and what data you want to traverse the pipe to your client application. In the first instance, Linq resolves the expression and pulls all of the role data as a precursor to
New.roles.ToDictionary(row => row.rolename, row => row.roleid);
At that point, the data moves from the DB into the client and is transformed into your dictionary. So far, so good.
The problem is that your second Linq expression is asking Linq to do the transform on the second DB using the dictionary on the DB to do so. In other words, it is trying to figure out a way to pass the entire dictionary structure to the DB so that it can select the correct ID value as part of the delayed execution of the query. I suspect that it would resolve just fine if you altered the second half to
var roles = from rl in Old.userrolelinks
join r in Old.roles on rl.RoleID equals r.RoleID
where rl.UserID == userId
select r.RoleName;
var list = roles.ToDictionary(roleName => roleName, newRoles[roleName]);
That way, it resolves your select on the DB (selecting just the rolename) as a precursor to processing the ToDictionary call (which it should do on the client as you'd expect). This is essentially exactly what you are doing in your second example because AsEnumerable is pulling the data to the client before using it in the ToList call. You could as easily change it to something like
var roles = from rl in Old.userrolelinks
join r in Old.roles on rl.RoleID equals r.RoleID
where rl.UserID == userId
select r;
var list = roles.AsEnumerable().Select(r => new Role { Name = r.RoleName, ID = newRoles[r.RoleName] });
and it'd work out the same. The call to AsEnumerable() resolves the query, pulling the data to the client for use in the Select that follows it.
Note that I haven't tested this, but as far as I understand Entity Framework, that's my best explanation for what's going on under the hood.

Jacob is totally right.
You can not transform the desired query without splitting it in two parts, because Entity Framework is unable to translate the get_Item call into the SQL query.
The only way is to write the LINQ to Entities query and then write a LINQ to Objects query to its result, just as Jacob advised.
The problem is Entity-Framework-specific one, it does not arise from our implementation of the Entity Framework support.