We are in the process of upgrading to NH3.1 which is going well -
everything is working as far as we can tell with existing code. One of
the motivations to move to NH3 from 2 has been to leverage the Linq
support and generally it is working really well. However I am
struggling with some more complex where clauses, specifically when I
want to check based on a sub-collection:
var results = from r in registrations
where (
from p in persons
where p.ExplicitManagers.Any(m => m.Manager == manager)
select p
).Contains(r.Registrant)
select r;
where the model is:
p is a Person and a registration r has a registrant of type Person
p contains a collection of ExplicitManager associative entities which
hold a reference to another Person (manager).
note: registrations is an IQueryable<Registration>.Query() and persons
in an IQueryable<Person>.Query().
Essentially I am trying to restrict the registrations to where person1
is an explicit manager of p. I can do this via joins but not through
the Contains subquery.
I get the following error:
"System.InvalidOperationException :
Sequence contains more than one
matching element"
the reason for doing this as a sub-query is because ultimately I need
to externalize the logic for checking the managers to make it reusable
(it actually is more complex but I have simplified it for this example
because it is the Any within a Contains which is causing the grief).
Contains seems to work fine when not having a sub-query with Any.
Is this something I am doing wrong, or is it something unsupported or
a bug, and is there another way of achieving the same thing?
Many thanks for any help you can give.
Whilst Contains doesn't seem to work properly, using Any does:
var results = from r in registrations
where (
from p in persons
where p.ExplicitManagers.Any(m => m.Manager == manager)
select p
).Any(p=>p == r.Registrant)
select r;
Can you execute the sub query on its own without problems?
var result = from p in persons
where p.ExplicitManagers.Any(m => m.Manager == manager)
select p;
Related
I have an EntityCollection ec in C# which has been populated with all Accounts.
Now I want another List or EntityCollection from ec which has all the accounts with status active.
I am using Linq for the same.
But both form of LINQ returns a an empty result while ec has 354 number of records
var activeCRMEC = (from cl in ec.Entities
where cl.Attributes["statecode"].ToString()=="0"
select cl);
OR
var activeCRMEC = ec.Entities.Where(x => x.Attributes["statecode"].ToString() == "0");
Each time the resultset is empty and I am unable to iterate over it. And 300 or so accounts are active, I have checked.
Same thing happens when I use some other attribute such as name etc.
Please be kind enough to point out my mistake.
You can Generate Early Bound Classes to write Linq Queries.
or Else
You can Write Linq Queries Using Late Bound Using OrganizationServiceContext Class.
For Your Reference:
OrganizationServiceContext OrgServiceCOntext = new OrganizationServiceContext(service);
var RetrieveAll = OrgServiceCOntext.CreateQuery("account").
ToList().Where(w => (w.GetAttributeValue<OptionSetValue>("statecode").Value ==0)).Select(s=>s);
I'll give you a few hints, and then tell you what I'm guessing your issue is.
First, use early bound entities. If you've never generated them before, use the earlybound generator, you'll save yourself a lot headaches.
Second, if you can't use early bound entities, use the GetAttribute() method on the Entity class. It'll convert types for you, and handle null reference issues.
Your LINQ expressions look to be correct, so either the ec.Entities doesn't have any entities in it that match the criteria of "statecode" equaling 0, or you possibly have some differed execution occurring on your IEnumerables. Try calling ToList() on the activeCRMEC immediately after the LINQ statement to ensure that is not your issue.
The statecode is an OptionSetValue, you should cast it in this way
((OptionSetValue)cl.Attributes["statecode"]).Value == 0
or
cl.GetAttributeValue<OptionSetValue>("statecode").Value == 0
Both ways are valid and you should ask for the Value that it is an int.
Hope this can help you.
I am having an odd problem with data loading which I don't understand, and I am hoping someone can explain to me what is going on, and perhaps how to accomplish my task more directly.
I am building a website using the technologies listed in the subject of this question.
I have a set of objects - each object has several properties (Name, ID, etc.) and a collection (ICollection<>) of other objects. So just looking at the tree of objects and their collections, it looks like this:
Tab
-TabRows
--Sections
---SectionRow
----Article
(So each tab has one or more tabrows, each tabrow has one or more sections, and so on. Each sub-object has a link back the parent, so each sectionrow has a SectionID, each Section has a TabRowID, etc.)
OK, so given that structure, consider this code:
// GET api/Tab/5
public Tab GetTab(int id)
{
var tab = db.Tabs.FirstOrDefault(t => t.TabId == id);
var tabrows = db.TabRows.ToList();
var sections = db.Sections.ToList(); // This makes the tabRow.Sections populate
var sectionrows = db.SectionRows.ToList();
var articles = db.Articles.ToList();
return tab;
}
So here is what happens. When the first line (var tab =...) executes, I get a tab object, but the TabRows collection is empty. (It is not null because the constructor instantiates it).
When the second line (var tabrows =...) executes, tab.TabRows suddenly populates. tab.TabRows.Sections is empty.
When the third line executes, tab.TabRows.Sections suddenly populates.
And so on.
I am assuming this is some sort of "lazy loading" on behalf of Linq, or perhaps one of the other technologies. But I don't know them well enough to figure it out.
Is there a way to re-write this so that I can just call line 1 and basically have everything auto-populate without having to individually reference every single object in every single collection?
Lazy loading is enabled by default and eager loading disabled. Entity framework allows you to hint at eager loading using the include statements. Your statement will become something like this.
var tab = db.Tabs.FirstOrDefault(t => t.TabId == id).Include("TabRows");
or as Include(t => t.TabRows);
Take a look at this link for more information.
In your case you would need to handle nested includes as well. Which means you would be better off taking another Model (your class) structured as follows
Tabs -> Containing a List<TabRows> -> containing a List<Sections> etc.
You would then need to re-write the linq so it populates the entire Model including the nested entities using nested includes.
As a side note, too many of these inner joins might slow down your querying and so consider indexed views on your DB side if and when possible
I'm using Grails with an Oracle database. Most of the data in my application is part of a hierarchy that goes something like this (each item containing the following one):
Direction
Group
Building site
Contract
Inspection
Non-conformity
Data visible to a user is filtered according to his accesses which can be at the Direction, Group or Building Site level depending on user role.
We easily accomplished this by creating a listWithSecurity method for the BuildingSite domain class which we use instead of list across most of the system. We created another listWithSecurity method for Contract. It basically does a Contract.findAllByContractIn(BuildingSite.listWithSecurity). And so on with the other classes. This has the advantage of keeping all the actual access logic in BuildingSite.listWithsecurity.
The problem came when we started getting real data in the system. We quickly hit the "ora-01795 maximum number of expressions in a list is 1000" error. Fair enough, passing a list of over 1000 literals is not the most efficient thing to do so I tried other ways even though it meant I would have to deport the security logic to each controller.
The obvious way seemed to use a criteria such as this (I only put the Direction level access here for simplicity):
def c = NonConformity.createCriteria()
def listToReturn = c.list(max:params.max, offset: params.offset?.toInteger() ?: 0)
{
inspection {
contract {
buildingSite {
group {
'in'("direction",listOfOneOrTwoDirections)
}
}
}
}
}
I was expecting Grails to generate a single query with joins that would avoid the ora-01795 error but it seems to be calling a separate query for each level and passing the result back to Oracle as literal in an 'in' to query the other level. In other words, it does exactly what I was doing so I get the same error.
Actually, it might be optimising a bit. It seems to be solving the problem but only for one level. In the previous example, I wouldn't get an error for 1001 inspections but I would get it for 1001 contracts or building sites.
I also tried to do basically the same thing with findAll and a single HQL where statement to which I passed a single direction to get the nonConformities in one query. Same thing. It solves the first levels but I get the same error for other levels.
I did manage to patch it by splitting my 'in' criteria into many 'in' inside an 'or' so no single list of literals is more than 1000 long but that's profoundly ugly code. A single findAllBy[…]In becomes over 10 lines of code. And in the long run, it will probably cause performance problems since we're stuck doing queries with a very large amount of parameters.
Has anyone encountered and solved this problem in a more elegant and efficient way?
This won't win any efficiency awards but I thought I'd post it as an option if you just plainly need to query a list of more than 1000 items none of the more efficient options are available/appropriate. (This stackoverflow question is at the top of Google search results for "grails oracle 1000")
In a grails criteria you can make use of Groovy's collate() method to break up your list...
Instead of this:
def result = MyDomain.createCriteria().list {
'in'('id', idList)
}
...which throws this exception:
could not execute query
org.hibernate.exception.SQLGrammarException: could not execute query
at grails.orm.HibernateCriteriaBuilder.invokeMethod(HibernateCriteriaBuilder.java:1616)
at TempIntegrationSpec.oracle 1000 expression max in a list(TempIntegrationSpec.groovy:21)
Caused by: java.sql.SQLSyntaxErrorException: ORA-01795: maximum number of expressions in a list is 1000
at oracle.jdbc.driver.T4CTTIoer.processError(T4CTTIoer.java:440)
You'll end up with something like this:
def result = MyDomain.createCriteria().list {
or { idList.collate(1000).each { 'in'('id', it) } }
}
It's unfortunate that Hibernate or Grails doesn't do this for you behind the scenes when you try to do an inList of > 1000 items and you're using an Oracle dialect.
I agree with the many discussions on this topic of refactoring your design to not end up with 1000+ item lists but regardless, the above code will do the job.
Along the same lines as Juergen's comment, I've approached a similar problem by creating a DB view that flattens out user/role access rules at their most granular level (Building Site in your case?) At a minimum, this view might contain just two columns: a Building Site ID and a user/group name. So, in the case where a user has Direction-level access, he/she would have many rows in the security view - one row for each child Building Site of the Direction(s) that the user is permitted to access.
Then, it would be a matter of creating a read-only GORM class that maps to your security view, joining this to your other domain classes, and filtering using the view's user/role field. With any luck, you'll be able to do this entirely in GORM (a few tips here: http://grails.1312388.n4.nabble.com/Grails-Domain-Class-and-Database-View-td3681188.html)
You might, however, need to have some fun with Hibernate: http://grails.org/doc/latest/guide/hibernate.html
I have a course table which I need to search based on keywords typed in the search box.
Here is a sample query:
SELECT * FROM Courses WHERE
Title LIKE '%word%' OR Title LIKE '%excel%' OR
Contents LIKE '%word%' OR Contents LIKE '%excel%'
How can I convert this in LINQ where LINQ would dynamically generate WHERE statements based on each keywords.
I tried to user PredicateBuilder it works fine as long as the field is VARCHAR. For the "TEXT" fields the quotes are not generated thus causing compiler to give an error message. Here is the SQL generated by PredicateBuilder
SELECT [t0].[CoursesID], [t0].[Title], [t0].[Contents], [t0].[Active],
FROM [dbo].[Courses] AS [t0]
WHERE ([t0].[Title] LIKE '%word%') OR ([t0].[Contents] LIKE %word%) OR
([t0].Title] LIKE '%excel%') OR ([t0].[Contents] LIKE %excel%)
Notice there is no single Quote for the "Contents" field which is a Text field in the database.
Is there any easy way to build WHERE statement and attach it with query? Does anyone know how I can do this without PredicateBuilder?
Thanks in advance.
Since you are working w/ LINQ I suppose you are working against a LINQ-to-SQL data context right? I don't have a spare DataContext lying around to test this, but this should give you some ideas.
I don't know if it will work against data context though, but most of these are pretty basic stuff (chaining OR operator and Contains method call) so it shouldn't cause problem when the query translates to SQL.
First I create a custom function that would build my predicate:
Func<string, Func<DataItem, bool>> buildKeywordPredicate =
keyword =>
x => x.Title.Contains(keyword)
|| x.Contents.Contains(keyword);
This is a function which takes a single string keyword and then return another function which takes a DataItem and checks it against the keyword.
Basically, if you pass in "Stack", you'll get a predicate: x => x.Title.Contains("Stack") || x.Contents.Contains("Stack").
Next, since there are many possible keywords and you need to chain it with an OR operation, I create another helper function to chain 2 predicates together with an OR
Func<Func<DataItem,bool>, Func<DataItem, bool>, Func<DataItem, bool>> buildOrPredicate =
(pred1, pred2) =>
x => pred1(x) || pred2(x);
This function takes 2 predicates and then join them up with an OR operation.
Having those 2 functions, I can then build my where predicate like this:
foreach (var word in keywords) {
filter = filter == null
? buildKeywordPredicate(word)
: buildOrPredicate(filter, buildKeywordPredicate(word));
}
The first line inside the loop basically checks if the filter is null. If it is, then we want a simple keyword filter built for us.
Else if the filter is not null, we need to chain existing filters with an OR operation, so we pass the existing filter and a new keyword filter to buildOrPredicate to do just that.
And then we can now create the WHERE part of the query:
var result = data.Where(filter);
Passing in the complicated predicate we've just built.
I don't know if this will different from using PredicateBuilder but since we are deferring query translation to the LINQ-to-SQL engine, there should not be any problems.
But as I said, I havn't tested it against a real data context, so if there's any problems you can write in the comments.
Here's the console app that I built to test: http://pastebin.com/feb8cc1e
Hope this helps!
EDIT: For a more generic and reusable version which involves properly utilizing the Expression Trees in LINQ, check out Thomas Petricek's blog post: http://tomasp.net/articles/dynamic-linq-queries.aspx
As predicate builder doesn't know the DB type of the property the Contains method is called on, I guess this might be a problem inside linq to sql. Have you tried with a normal query (not with predicate builder) and a TEXT column with Contains?
Okay, so I'm doing my first foray into using the ADO.NET Entity Framework.
My test case right now includes a SQL Server 2008 database with 2 tables, Member and Profile, with a 1:1 relationship.
I then used the Entity Data Model wizard to auto-generate the EDM from the database. It generated a model with the correct association. Now I want to do this:
ObjectQuery<Member> members = entities.Member;
IQueryable<Member> membersQuery = from m in members select m;
foreach (Member m in membersQuery)
{
Profile p = m.Profile;
...
}
Which halfway works. I am able to iterate through all of the Members. But the problem I'm having is that m.Profile is always null. The examples for LINQ to Entities on the MSDN library seem to suggest that I will be able to seamlessly follow the navigation relationships like that, but it doesn't seem to work that way. I found that if I first load the profiles in a separate call somehow, such as using entities.Profile.ToList, then m.Profile will point to a valid Profile.
So my question is, is there an elegant way to force the framework to automatically load the data along the navigation relationships, or do I need to do that explicitly with a join or something else?
Thanks
Okay I managed to find the answer I needed here http://msdn.microsoft.com/en-us/magazine/cc507640.aspx. The following query will make sure that the Profile entity is loaded:
IQueryable<Member> membersQuery = from m in members.Include("Profile") select m;
I used this technique on a 1 to many relationship and works well. I have a Survey class and many questions as part of that from a different db table and using this technique managed to extract the related questions ...
context.Survey.Include("SurveyQuestion").Where(x => x.Id == id).First()
(context being the generated ObjectContext).
context.Survey.Include<T>().Where(x => x.Id == id).First()
I just spend 10mins trying to put together an extention method to do this, the closest I could come up with is ...
public static ObjectQuery<T> Include<T,U>(this ObjectQuery<T> context)
{
string path = typeof(U).ToString();
string[] split = path.Split('.');
return context.Include(split[split.Length - 1]);
}
Any pointers for the improvements would be most welcome :-)
On doing a bit more research found this ... StackOverflow link which has a post to Func link which is a lot better than my extension method attempt :-)