Is there anyway to use NHibernate in such a way that it whould only execute the query/queries once the returned object of a query/statement is used.. just like EF doest it?
For most instances with EF it wont send and execute the actual query to the database until the returned object of a linq-"statement" is used.. for instance:
var x = for e in entities.MyTable
select e;
This aint executed yet!
Which meens that Im able to mofidy the x-objects "linq-query" however I like without actualt "pulling" any data from the database:
x = x.Where(i=>i.SomeThing = someThing);
Still aint executed!
x.ToList<MyTable>()
Now its executed!
But in NHibernate the query gets executed once the transaction gets closed or commited from what I have understod.. and in most cases thats done already in the repository. So you can't simply in any other place alter the query and then send it to the database. Cause the query is already sent and that whould mean that you later on only whould alter whats "displayed" from the result.
I might have gotten this al wrong so please correct me if I am wrong.
Huge thanks in advance!
You can try something like this using detached QueryOver
var query = QueryOver.Of<Customer>()
.Where(x => x.LastName == "Smith"); // query is not executed yet
query.GetExecutableQueryOver(session).List();
Good thing is that you can pass QueryOver objects and get it executed somewhere else.
Related
I am starting to dabble in CI4's rc... trying to get a head of the game. I noticed that the Model is completely rewritten.
Going through their documentation, I need some guidance on how to initiate the equivalent DB query builder in CI4.
I was able to leverage return $this->findAll(), etc...
however, need to be able to be able to query w/ complex joins and also be able to return single records etc...
When trying something like
return $this->orderBy('import_date', 'desc')
->findColumn('import_date')
->first();
but getting error:
Call to a member function first() on array
Any help or guidance is appreciated.
Suppose you have a model instantiated as
$userModel = new \App\Models\UserModel;
Now you can use it to get a query builder like.
$builder = $userModel->builder();
Use this builder to query anything for e.g.
$user = $builder->first();
Coming to your error.
return $this->orderBy('import_date', 'desc')
->findColumn('import_date');
findColumn always returns an array or null. So you can't use it as object. Instead you should do following.
return $this->orderBy('import_date', 'desc')->first();
I'm missing something simple - I do not want to access the results of this query in a view.
Here is the query:
#adm = Admin.where({:id => {"$ne" => params[:id].to_s},:email => params[:email]})
And of course when you inspect you get:
#adm is #<MongoMapper::Plugins::Querying::DecoratedPluckyQuery:0x007fb4be99acd0>
I understand (from asking the MM guys) why this is the case - they wished to delay the results of the actual query as long as possible, and only get a representation of the query object until we render (in a view!).
But what I'm trying to ascertain in my code is IF one of my params matches or doesn't match the result of my query in the controller so I can either return an error message or proceed.
Normally in a view I'm going to do:
#adm.id
To get the BSON out of this. When you try this on the Decorated Query of course it fails:
NoMethodError (undefined method `id' for #<MongoMapper::Plugins::Querying::DecoratedPluckyQuery:0x007fb4b9e9f118>)
This is because it's not actually a Ruby Object yet, it's still the query proxy.
Now I'm fundamentally missing something because I never read a "getting started with Ruby" guide - I just smashed my way in here and learned through brute-force. So, what method do I call to get the results of the Plucky Query?
The field #adm is set to a query as you've seen. So, to access the results, you'll need to trigger execution of the query. There are a variety of activation methods you can call, including all, first, and last. There's a little documentation here.
In this case, you could do something like:
adm_query = Admin.where({:id => {"$ne" => params[:id].to_s},:email => params[:email]})
#adm_user = adm_query.first
That would return you the first user and after checking for nil
if #adm_user.nil?
# do something if no results were found
end
You could also limit the query results:
adm_query = Admin.where( ... your query ...).limit(1)
I want to use Second level Cache for my query with eager loading(query is below wrote in 3 different ways, i use query cache). I have standard one to many association. I set entity cache for parent, child, and association between parent and class. And the 2nd level cache doesn't work because i got exceptions.
I wrote my query in 3 different way:
Criteria:
session.CreateCriteria<DictionaryMaster>().SetFetchMode("DictionaryItems", FetchMode.Eager)
.SetResultTransformer(new DistinctRootEntityResultTransformer())
.SetCacheable(true).SetCacheMode(CacheMode.Normal)
.List<DictionaryMaster>().ToList();
When I invoked this query i got exception "Unable to perform find[SQL: SQL not available]"
I think that the problem exists because I use DistinctRootEntityResultTransformer transform. I will start create my custom transform class and I hope that will work.
Query over:
session.QueryOver<DictionaryMaster>().Fetch(x => x.DictionaryItems).Eager
.TransformUsing(new DistinctRootEntityResultTransformer())
.Cacheable().CacheMode(CacheMode.Normal)
.List<DictionaryMaster>().ToList();
Exception is the same as in Criteria.
Linq:
session.Query<DictionaryMaster>().Fetch(x => x.DictionaryItems).Cacheable().CacheMode(CacheMode.Normal).ToList();
Here error depends from the version of nhibernate in 3.1 a got this error https://nhibernate.jira.com/browse/NH-2587?page=com.atlassian.jira.plugin.system.issuetabpanels%3Achangehistory-tabpanel
but in 3.2 version i got this: https://nhibernate.jira.com/browse/NH-2856
Thanks in advance
sJHony I have found solution, but for me is more like workaround. Therefore if you know any other solution give me sign.
I utilize QueryOver without any transformation, the fault of this solution is that the query return elements equal amount of childs. Next I retrieve not multiplied list in memory using distinct.
This solution is ok, but when we add one more Fetch for query, then collection in object also be multiplied, that is why i modified collection type from IList(Bag) to ISet(Set).
Code looks like:
var queryCacheResult =
session.QueryOver<DictionaryMaster>()
.Fetch(x => x.DictionaryItems).Eager
.Cacheable().CacheMode(CacheMode.Normal)
.List<DictionaryMaster>().ToList();
return queryCacheResult.Distinct(new KeyEqualityComparer<DictionaryMaster>(x => x.Code)).ToList();
I have a simple unit test where I execute the same NHibernate named query 2 times (different session each time) with the identical parameter. It's a simple int parameter, and since my query is a named query I assume these 2 calls are identical and the results should be cached.
In fact, I can see in my log that the results ARE being cached, but with different keys. So, my 2nd query results are never found in cache.
here's a snip from my log (note how the keys are different):
(first query)
DEBUG NHibernate.Caches.SysCache2.SysCacheRegion [(null)] <(null)> -
adding new data: key= [snipped]... parameters: ['809']; named
parameters: {}#743460424 &
value=System.Collections.Generic.List`1[System.Object]
(second query)
DEBUG NHibernate.Caches.SysCache2.SysCacheRegion [(null)] <(null)> -
adding new data: key=[snipped]... parameters: ['809']; named
parameters: {}#704749285 &
value=System.Collections.Generic.List`1[System.Object]
I have NHibernate set up to use the query cache. And I have these queries set to cacheable=true. Don't know where else to look. Anyone have any suggestions?
Thanks
-Mike
Okay - i figured this out. I was executing my named query using the following syntax:
IQuery q = session.GetNamedQuery("MyQuery")
.SetResultTransformer(Transformers.AliasToBean(typeof(MyDTO)))
.SetCacheable(true)
.SetCacheRegion("MyCacheRegion");
( which, I might add, is EXACTLY how the NHibernate docs tell you how to do it.. but I digress ;) )
If you use create a new AliasToBean Transformer for every query, then each query object (which is the key to the cache) will be unique and you will never get a cache hit. So, in short, if you do it like the nhib docs say then caching wont work.
Instead, create your transformer one time in a static member var and then use that for your query, and caching will work - like this:
private static IResultTransformer myTransformer = Transformers.AliasToBean(typeof(MyDTO))
...
IQuery q = session.GetNamedQuery("MyQuery")
.SetResultTransformer(myTransformer)
.SetCacheable(true)
.SetCacheRegion("MyCacheRegion");
With many HQL queries, time and time again I am getting this exception:
Antlr.Runtime.NoViableAltException
This is really generic and unhelpful - does anyone know how best to debug this? Obviously it's a problem with my HQL - but without any clue as to what exactly is wrong it's very much a case of trial and error. I'm pulling my hair out every time I see this.
Note, I don't want to post any HQL here, becuase it's something that I am often coming across, not a problem related to one query.
Does anyone know the best way to tackle this? Is there any tool for validating HQL queries?
Have a look at NHibernate Query Analyzer. It is not perfect, but it will be helpful in many situations.
I can't help you directly, here's something I can share.
When dealing with hibernate or nhibernate (NH), I generally debug by enabling logging on the nhibernate's log4net, or/and the logging of queries at the DB side (e.g. mysql).
They can tell me what is the queries being formulated and executed at the DB and what are the exceptions thrown back by the DB.
For instance, if you have the following error:
Exception of type 'Antlr.Runtime.NoViableAltException' was thrown. near line 1, column
745 [select afe.AFEDataId, afe.Name, afe.AdditionalDescription, afe.ProjectType,
afe.BusinessUnit, afe.plantId, afe.fuelTypeId, afe.DisplayStatus, afe.BudgetedAmount,
sum(exp.Amount), afe.CreatedDate from Company.AFE.Model.AFEData as afe inner join
afe.Expenditures as exp inner join exp.ExpenditureType where (afe.Status.StatusId =
:statusId) and (afe.IsRestrictedVisibility = false OR (select count(AFEDataId) from
Company.AFE.Model.Reader as r where r.AFEData.AFEDataId = afe.AFEDataId AND
r.Contact.ContactId = '70bc6350-c466-40d5-a067-9d1f00bed7dc') > 0 OR (select count(AFEDataId)
from Company.AFE.Model.Editor as e where e.AFEData.AFEDataId = afe.AFEDataId AND
e.Contact.ContactId = '70bc6350-c466-40d5-a067-9d1f00bed7dc') > 0 OR 1=1) afe.AFEDataId,
afe.Name, afe.AdditionalDescription, afe.ProjectType, afe.BusinessUnit, afe.plantId,
afe.fuelTypeId, afe.DisplayStatus, afe.BudgetedAmount, afe.CreatedDate order by afe.Name ASC]
Go and look at character 745 from the original query that was provided and check to see if there is a spelling error, as there was in this one that I just looked at.
Which version of NH you used, for the latest version, the query exchange has some updated, such as you can't use "count(1)" in query, must change to count([alias name]), NH will translate to "select class.id from ... "