I am running a Linq to SQL query in Entity Framework and it is giving me a StackOverflowException. So I thought, this has to be the perfect website to ask this question. But I see two other questions here about a StackOverflowException in Entity Framework and they got no answers. Anyway, I'll give this a try. My query was working, but I want to insert some spacer columns that will be loaded into my Telerik Spreadsheet control. My search on StackOverflow told me how to enter static columns in my query and now every time I try to run it I get the a StackOverflowException. Below is a sample of my query. Can you tell me how to correct this? If I remove the Spacer_1 column the error goes away, but I need a spacer column.
using (var context = new MyEntities())
{
var query = context.MyTable
.Where(o => o.id == idValue)
.Select(o => new {
o.RealColumn1,
o.RealColumn2,
o.RealColumn3,
Spacer_1 = "",
o.RealColumn4,
o.RealColumn5
});
var list = query.ToList();
}
Related
I want to fetch the candidate and the work exp where it is not deleted. I am using repository pattern in my c# app mvc.
Kind of having trouble filtering the record and its related child entities
I have list of candidates which have collection of workexp kind of throws error saying cannot build expression from the body.
I tried putting out anonymous object but error still persist, but if I use a VM or DTO for returning the data the query works.
It's like EF doesn't like newing up of the existing entity within its current context.
var candidate = dbcontext.candidate
.where(c=>c.candiate.ID == id).include(c=>c.WorkExperience)
.select(e=>new candidate
{
WorkExperience = e.WorkExperience.where(k=>k.isdeleted==false).tolist()
});
Is there any workaround for this?
You cannot call ToList in the expression that is traslated to SQL. Alternatively, you can start you query from selecting from WorkExperience table. I'm not aware of the structure of your database, but something like this might work:
var candidate = dbcontext.WorkExperience
.Include(exp => exp.Candidate)
.Where(exp => exp.isdeleted == false && exp.Candidate.ID == id)
.GroupBy(exp => exp.Candidate)
.ToArray() //query actually gets executed and return grouped data from the DB
.Select(groped => new {
Candidate = grouped.Key,
Experience = grouped.ToArray()
});
var candidate =
from(dbcontext.candidate.Include(c=>c.WorkExperience)
where(c=>c.candiate.ID == id)
select c).ToList().Select(cand => new candidate{WorkExperience = cand.WorkExperience.where(k=>k.isdeleted==false).tolist()});
In the following example, we insert an entity called taskinstance to our context. we have a foreign key FK_Contract that we set at 2.
entity.FK_Contract = 2;
context.TaskInstances.AddObject(entity);
The query generated by entity framework is a simple insert. (everything is fine)
However, the following query works differently.
int contractId = context.Contracts.Where((T) => T.Name == contractName).Single().Id;
entity.FK_Contract = contractId;
context.TaskInstances.AddObject(entity);
In the trace created by entity framework we see without surprise the query selecting the Id according a contractName but we also see an extra request looking like:
select id,... from [TaskInstances] WHERE [Extent1].[FK_Task] = #contractId
This extra query leads to many problems, especially when we work with a foreign table with millions of record. The network goes down!
Therefore we 'd like to figure out the purpose of this extra query and the way to make it disappear.
It looks like the extra query is populating a collection of tasks on the returned Contract object. Try projecting just the column you want:
int contractId = context.Contracts
.Where(T => T.Name == contractName)
.Select(T => T.Id)
.Single();
This is my real world example.
I have 4 tables:
Person
Plan
Coverage
CoveredMembers
Each person can have many plans, each of those plans can have many coverages. Each of those coverages can have many CoveredMembers.
I need a query that will apply a filter on Plan.PlanType == 1 and CoveredMembers.TermDate == null.
This query should bring back any person who has a medical type plan that is not terminated.
This SQL statement would do just that:
SELECT Person.*, Plans.*, Coverages.*, CoveredMembers.*
FROM Person P
INNER JOIN Plan PL ON P.PersonID = PL.PersonID
INNER JOIN Coverage C on PL.PlanID = C.PlanID
INNER JOIN CoveredMember CM on C.CoverageID = CM.CoverageID
WHERE CM.TermDate = NULL AND PL.PlanType = 1
I have figured out how to do this using anonymous types, but I sometimes need to update the data and save back to the database - and anonymous types are read only.
I was given a solution that did work using JOIN but it only brought back the persons (albeit filtered the way I needed). I can then loop through each person:
foreach (var person in persons) {
foreach (var plan in person.Plans{
//do stuff
}
}
But wouldn't that make a db call for each iteration of the loop? I have 500 persons with 3 unterminated medical plans each, so it would call the db 1500 times?
This is why I want to bring the whole data tree from Persons to CoveredMembers back in one shot. Is this not possible?
I believe this is accomplished in two parts:
Your query to determine the people you wish to have returned based on your criteria as discussed in this question previously: Entity framework. Need help filtering results
Properly setting the navigation properties for entities you want brought together to be eagerly loaded: http://msdn.microsoft.com/en-us/data/jj574232.aspx
For example if your Person entity looks like:
public class Person {
public List<Plan> Plans {get; set;}
...
}
When returning data from the dbcontext you can also use explicit eager loading with the include option:
var people = context.People
.Include(p => p.Plans)
.ToList();
....
If these are nested - coverage is part of plan, etc (which it looks like, it goes something like):
var people = context.People
.Include(p => p.Plans.Select(pl=>pl.Coverage).Select(c=>c.CoveredMembers)))
.ToList();
....
I am making some assumptions about your data model here, and my code above probably needs a little tweaking.
EDIT:
I might need someone else to weigh in here, but I don't think you can add the where clause into an include like that (my example above leads you that way a bit by putting the include on the context object, instead return an IQueryable with your conditions set as solved in your first post (without a ToList() called on it) and then use the code you wrote above without the Where clauses:
From first post (you supplied different criteria in this one, but same concept)
var q = from q1 in dbContext.Parent
join q2 in dbContext.Children
on q1.key equals q2.fkey
join q3 in ........
where q4.col1 == 3000
select q1;
Then:
List<Person> people = q.Include(p => p.Plans
.Select(pl => pl.Coverages)
.Select(c => c.CoveredMembers).ToList();
Again, doing this without being able to troubleshoot - I am sure it would take me a few attempts to iron this one out too.
I have been trying to figure out how to optimize the following query for the past few days and just not having much luck. Right now my test db is returning about 300 records with very little nested data, but it's taking 4-5 seconds to run and the SQL being generated by LINQ is awfully long (too long to include here). Any suggestions would be very much appreciated.
To sum up this query, I'm trying to return a somewhat flattened "snapshot" of a client list with current status. A Party contains one or more Clients who have Roles (ASPNET Role Provider), Journal is returning the last 1 journal entry of all the clients in a Party, same goes for Task, and LastLoginDate, hence the OrderBy and FirstOrDefault functions.
Guid userID = 'some user ID'
var parties = Parties.Where(p => p.BrokerID == userID).Select(p => new
{
ID = p.ID,
Title = p.Title,
Goal = p.Goal,
Groups = p.Groups,
IsBuyer = p.Clients.Any(c => c.RolesInUser.Any(r => r.Role.LoweredName == "buyer")),
IsSeller = p.Clients.Any(c => c.RolesInUser.Any(r => r.Role.LoweredName == "seller")),
Journal = p.Clients.SelectMany(c => c.Journals).OrderByDescending(j => j.OccuredOn).Select(j=> new
{
ID = j.ID,
Title = j.Title,
OccurredOn = j.OccuredOn,
SubCatTitle = j.JournalSubcategory.Title
}).FirstOrDefault(),
LastLoginDate = p.Clients.OrderByDescending(c=>c.LastLoginDate).Select(c=>c.LastLoginDate).FirstOrDefault(),
MarketingPlanCount = p.Clients.SelectMany(c => c.MarketingPlans).Count(),
Task = p.Tasks.Where(t=>t.DueDate != null && t.DueDate > DateTime.Now).OrderBy(t=>t.DueDate).Select(t=> new
{
ID = t.TaskID,
DueDate = t.DueDate,
Title = t.Title
}).FirstOrDefault(),
Clients = p.Clients.Select(c => new
{
ID = c.ID,
FirstName = c.FirstName,
MiddleName = c.MiddleName,
LastName = c.LastName,
Email = c.Email,
LastLogin = c.LastLoginDate
})
}).OrderBy(p => p.Title).ToList()
I think posting the SQL could give us some clues, as small things like the order of OrderBy coming before or after the projection could make a big difference.
But regardless, try extracting the Clients in a seperate query, this will simplify your query probably. And then include other tables like Journal and Tasks before projecting and see how this affects your query:
//am not sure what the exact query would be, and project it using ToList()
var clients = GetClientsForParty();
var parties = Parties.Include("Journal").Include("Tasks")
.Where(p=>p.BrokerID == userID).Select( p => {
....
//then use the in-memory clients
IsBuyer = clients.Any(c => c.RolesInUser.Any(r => r.Role.LoweredName == "buyer")),
...
}
)
In all cases, install EF profiler and have a look at how your query is affected. EF can be quiet surprising. Something like putting OrderBy before the projection, the same for all these FirstOrDefault or SingleOrDefault, they can all have a big effect.
And go back to the basics, if you are searching on LoweredRoleName, then make sure it is indexed so that the query is fast (even though that could be useless since EF could end up not making use of the covering index since it is querying so many other columns).
Also, since this is query is to view data (you will not alter data), don't forget to turn off Entity tracking, that will give you some performance boost as well.
And last, don't forget that you could always write your SQL query directly and project to your a ViewModel rather than anonymous type (which I see as a good practice anyhow) so create a class called PartyViewModel that includes the flatten view you are after, and use it with your hand-crafted SQL
//use your optimized SQL query that you write or even call a stored procedure
db.Database.SQLQuery("select * from .... join .... on");
I am writing a blog post about these issues around EF. The post is still not finished, but all in all, just be patient, use some of these tricks and observe their effect (and measure it) and you will reach what you want.
First I'd like to show the corresponding code snippet. When it comes to objCtx.AttachTo() it throws me an error:
Error: "The object cannot be attached because the value of a property that is a part of the EntityKey does not match the corresponding value in the EntityKey."
// convert string fragIds to Guid fragIds
var fragIdsGuids = docGenResult.FragIds.Select(c => new Guid(c)).ToList();
//add each fragment to document))))
foreach (Guid fragIdsGuid in fragIdsGuids)
{
var fragment = new Fragment() { EntityKey = new EntityKey("DocTestObjectContext.Fragments", "ID", fragIdsGuid) };
objCtx.AttachTo("Fragments", fragment);
}
objCtx.SaveChanges();
I've checked everything and I'm not missing any primary key.
However I need some words to explain why I think I have to do it this way.
I'm using EF4 in a C# Environment.
I have a many to many relationship between two tables, Document and Fragments(Primary key "ID") (Documents can have many fragments and a fragment can be a part of many documents)
The Entity Model works fine for me.
However when I try to add a new document to the DB I already have the IDs of the related Fragments in my hand. For adding a new document to the DB I have to call each Fragmentobject and add it to the mapped reference in my document-object. This is a bottleneck because a document can have more than 1000 fragments. The Consequence is that I need 1sec per document. Not much, but I have to create more than 3000 documents and saving this second would result in more speed.
Hopefully you know what's wrong in here.
Thanks.
Thomas
1st edit:
here is the solution wich actually works. I would like to avoid to load all the fragments and instead just save the fragment GUID I already have in the mapping table.
// convert string fragIds to Guid fragIds
var fragIdsGuids = docGenResult.FragIds.Select(c => new Guid(c)).ToList();
// get responding entities from Fragment table
var fragmentList = objCtx.Fragments.Where(c => fragIdsGuids.Contains(c.ID)).ToList();
foreach (var fragment in fragmentList)
{
doc.Fragment.Add(fragment);
}
objCtx.SaveChanges();
2nd edit:
I have the feeling that it is not really clear what I try to do.
However I would like to link/reference existing fragments in a Fragment-table to a coressponding Document in a Document table. The Document I'd like to reference is a new one. The document to Fragment table has an many to many relationship. This relationship has a linking table on the database. In the model it is correctly modeled as a many to many relationship. That's fine.
So far so good. What works is what you can see under my first edit. I have to load all the necessary fragments for a document by their id
// get responding entities from Fragment table
var fragmentList = objCtx.Fragments.Where(c => fragIdsGuids.Contains(c.ID)).ToList();
After that I'm able to add them to my document entity:
foreach (var fragment in fragmentList)
{
doc.Fragment.Add(fragment);
}
But why the hell do I have to load the whole entity (fragments) only to link it to a new document. Why do not tell the EntityStateManager "Dude, here you have some Fragment IDs, link them!"?
Further I tried to follow the MSDN article mentioned by Adrian in the comments. This doesn't worked out for me.
I'll try this:
var fragment = new Fragment {ID = fragIdsGuid};
//fragment.EntityKey.Dump(); // -- this should be null
objCtx.AttachTo("Fragments", fragment);
//fragment.EntityKey.Dump(); // -- shows the EntityKey object, created after the object is attached
The Dump function is from LinqPad