I have this tables in my data base:
Videos(IDVideo, Name...)
Episodes(IDEpisode, Name...)
Versions(IDVersion, Name, ....)
VideosVersions(IDVideo, IDEpisode, IDVersion)
A version can be for a video or for the episode and the relation in both cases is N:N, a video can have many versions and a version can be asigned to many videos or episodes.
In my edmx model has the four tables.
When I try to assign a new version to a video for example I use this code:
VideosVersions myVideoVersion = new VideosVersions();
myVideoVersion.IDVideo = paramVideo.IDVideo;
myVideoVersion.IDVersion = paramVersion.IDVersion;
myContext.VideosVersions.Add(myVideosVersions);
myContext.SaveChanges();
But I get the following exception:
Unable to update the EntitySet 'VideosVersions' because it has a DefiningQuery and no <InsertFunction> element exists in the <ModificationFunctionMapping> element to support the current operation.
Why?
Thanks.
EDIT: in my entity in the edmx model the three properites has a key, so if I am not wrong, this means that the PK of the entity is the combination of the three fields, is correct?
The mapper probably couldn't figure out which columns should be the primary key of VideosVersions. This means it doesn't know how to insert new records and only provides the query method. Make sure you have the primary key properly defined on the table, then update the mapping.
Related
In case we had the model:
class Publication(models.Model):
title = models.CharField(max_length=30)
class Article(models.Model):
publications = models.ManyToManyField(Publication)
According to: https://docs.djangoproject.com/en/4.0/topics/db/examples/many_to_many/, to create an object we must have both objects saved before we can create the relation:
p1 = Publication(title='The Python Journal')
p1.save()
a1 = Article(headline='Django lets you build web apps easily')
a1.save()
a1.publications.add(p1)
Now, if we called delete in either of those objects the object would be removed from the DB along with the relation between both objects. Up until this point I understand.
But is there any way of doing that, if an Article is removed, then, all the Publications that are not related to any Article will be deleted from the DB too? Or the only way to achieve that is to query first all the Articles and then iterate through them like:
to_delete = []
qset = a1.publications.all()
for publication in qset:
if publication.article_set.count() == 1:
to_delete(publication.id)
a1.delete()
Publications.filter(id__in=to_delete).delete()
But this has lots of problems, specially a concurrency one, since it might be that a publication gets used by another article between the call to .count() and publication.delete().
Is there any way of doing this automatically, like doing a "conditional" on_delete=models.CASCADE when creating the model or something?
Thanks!
I tried with #Ersain answer:
a1.publications.annotate(article_count=Count('article_set')).filter(article_count=1).delete()
Couldn't make it work. First of all, I couldn't find the article_set variable in the relationship.
django.core.exceptions.FieldError: Cannot resolve keyword 'article_set' into field. Choices are: article, id, title
And then, running the count filter on the QuerySet after filtering by article returned ALL the tags from the article, instead of just the ones with article_count=1. So finally this is the code that I managed to make it work with:
Publication.objects.annotate(article_count=Count('article')).filter(article_count=1).filter(article=a1).delete()
Definetly I'm not an expert, not sure if this is the best approach nor if it is really time expensive, so I'm open to suggestions. But as of now it's the only solution I found to perform this operation atomically.
You can remove the related objects using this query:
a1.publications.annotate(article_count=Count('article_set')).filter(article_count=1).delete()
annotate creates a temporary field for the queryset (alias field) which aggregates a number of related Article objects for each instance in the queryset of Publication objects, using Count function. Count is a built-in aggregation function in any SQL, which returns the number of rows from a query (a number of related instances in this case). Then, we filter out those results where article_count equals 1 and remove them.
I have been exclusively using cypher queries of this client for Neo4j because there is no out of the box way of doing many things. One of those id to get nodes. There is no way to retrieve them without knowing their id, which is very low level. Any idea on how to run a
$client->findOne('property','value');
?
It should be straightforward but it isn't from the documentation.
Make Indexes on the properties you want to search, from a newly created $personNode
$personIndex = new \Everyman\Neo4j\NodeIndex($client, 'person');
$personIndex->add($personNode, 'name', $personNode->name);
Then later to search, the new PHP object $personIndex will reference the same, populated index as above.
$personIndex = new \Everyman\Neo4j\NodeIndex($client, 'person');
$match = $personIndex->findOne('name', 'edoceo');
I basically have the same problem as the following Composite key in Cassandra with Pig. The only difference is I try to query for a part of the composite key within the where_clause of pig.
The data structure is similar to the earlier mentioned issue, I'll copy some code/context to minimize the reading of that issue.
We have a CQL table that looks something like this:
CREATE table data (
occurday text,
seqnumber int,
occurtimems bigint,
unique bigint,
fields map<text, text>,
primary key ((occurday, seqnumber), occurtimems, unique)
)
Instead of querying for both the seqnumber and the occurday (as was the issue in previously mentioned issue) I try to query one of the keys.
If I execute this query as part of a LOAD from within Pig, however, things don't work.
-- Need to URL encode the query
data = LOAD 'cql://ks/data?where_clause=occurday%3D%272013-10-01%27' USING CqlStorage();
gives
java.lang.RuntimeException
at org.apache.cassandra.hadoop.cql3.CqlPagingRecordReader$RowIterator.executeQuery(CqlPagingRecordReader.java:665)
at org.apache.cassandra.hadoop.cql3.CqlPagingRecordReader$RowIterator.<init>(CqlPagingRecordReader.java:301)
at org.apache.cassandra.hadoop.cql3.CqlPagingRecordReader.initialize(CqlPagingRecordReader.java:167)
at org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.PigRecordReader.initialize(PigRecordReader.java:181)
at org.apache.hadoop.mapred.MapTask$NewTrackingRecordReader.initialize(MapTask.java:522)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:763)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:370)
at org.apache.hadoop.mapred.LocalJobRunner$Job.run(LocalJobRunner.java:212)
Caused by: InvalidRequestException(why:occurday cannot be restricted by more than one relation if it includes an Equal)
at org.apache.cassandra.thrift.Cassandra$prepare_cql3_query_result$prepare_cql3_query_resultStandardScheme.read(Cassandra.java:51017)
at org.apache.cassandra.thrift.Cassandra$prepare_cql3_query_result$prepare_cql3_query_resultStandardScheme.read(Cassandra.java:50994)
at org.apache.cassandra.thrift.Cassandra$prepare_cql3_query_result.read(Cassandra.java:50933)
at org.apache.thrift.TServiceClient.receiveBase(TServiceClient.java:78)
at org.apache.cassandra.thrift.Cassandra$Client.recv_prepare_cql3_query(Cassandra.java:1756)
at org.apache.cassandra.thrift.Cassandra$Client.prepare_cql3_query(Cassandra.java:1742)
at org.apache.cassandra.hadoop.cql3.CqlPagingRecordReader$RowIterator.prepareQuery(CqlPagingRecordReader.java:605)
at org.apache.cassandra.hadoop.cql3.CqlPagingRecordReader$RowIterator.executeQuery(CqlPagingRecordReader.java:635)
... 7 more
Basically my question is, what am I doing wrong or what don't I understand?
As I understand from CqlPagingRecorderReader Used when Partition Key Is Explicitly Stated
I should be able to query with just part of the partition key?
Also while reading
Add CqlRecordReader to take advantage of native CQL pagination
I get the impression this should be possible, but I am swimming around with (in my opinion) no clear direction on how to accomplish this.
Any help is very very welcome at this point.
Regards,
Lennart Weijl
PS.
I am running on Cassandra 2.0.9 with Pig 0.13.0
According to CASSANDRA-6311, I believe you need to apply the 6331-v2-2.0-branch.txt patch, recompile pig, and then update your LOAD statement to:
data = LOAD 'cql://ks/data?where_clause=occurday%3D%272013-10-01%27' USING CqlInputFormat();
The key change being USING CqlInputFormat() which triggers the use of the new CqlRecordReader that was released in Cassandra 2.0.7.
Edit: Note that the exception is thrown from CqlPagingRecordReader which means you're still using the old record reader.
I have an audited entity A. Entity A holds field 'name' and a collection of entities B (annotated as Many-to-many relationship). I created an instance of A, defined name, collection of entities B and save all it into DB. This is revision #1. Then I changed name of A and update it in DB. This is revision #2.
I use the following method to get all entities of class A at revision #2
List<A> list = getAuditReader().createQuery().forEntitiesAtRevision(A.class, 2)
.add(AuditEntity.revisionNumber().eq((int) revisionId)).getResultList();
I get entity A at revision #2, but Envers also fetches collection of entities B related to this A from revision #1. Here an example of query used by Envers:
SELECT a_b_aud.a_id, a_b_aud.b_id
FROM a_b_aud CROSS JOIN b_aud
WHERE a_b_aud.b_id=b_aud.id
AND b_aud.rev=(SELECT max(b_aud2.rev)) FROM b_aud AS b_aud2 WHERE b_aud2.rev<=2 AND b_aud.id=b_aud2.id)
AND a_b_aud.rev=(SELECT max(a_b_aud2.rev)) FROM a_b_aud AS a_b_aud2 WHERE a_b_aud2.rev<=2 AND a_b_aud.a_id=a_b_aud2.a_id AND a_b_aud.b_id=a_b_aud2.b_id)
But actually I need NULL as a collection of entities B in case of there were no changes for it at revision #2 (because of performance issue).
There are two subselects in this query. And if we have more then one collection of entities related to A (C, D, E, F) and for about 100 thousands rows for each b_aud and a_b_aud the query above takes a lot of time.
I defined entity B as not audited (i.e. did not add #Audited annotation into B) and defined A B relation by the following:
#ManyToMany
#Cascade({org.hibernate.annotations.CascadeType.SAVE_UPDATE})
#JoinTable(name = "a_b", joinColumns = #JoinColumn(name = a_id))
#Audited(targetAuditMode = RelationTargetAuditMode.NOT_AUDITED)
public Set<B> getBs();
It fixes first SUBSELECT.
But I can not find standard solution to not query B's if it do not exist for requested revision (in my case #2). So the query should look like:
SELECT a_b_aud.a_id, a_b_aud.b_id
FROM a_b_aud CROSS JOIN b_aud
WHERE a_b_aud.b_id=b_aud.id b_aud.rev=2 AND a_b_aud.rev=2
The only solution I found is using native sql query and to execute it using hibernate template. Then convert result values into entity A using ResultTransformer.
Could anybody help with this issue? Is there a standard configuration/annotation I need to add to avoid second SUBSELECT?
There's no option in Envers not to load related entities when requested. Not however, that the B entities are always loaded lazily (regardless of the annotations on the relation), so if you don't want to execute the query which loads them, simply do not access that field.
If you want better read performance, you may also want to look at the validity audit strategy, see http://docs.jboss.org/hibernate/core/4.1/devguide/en-US/html/ch15.html#d5e4085. It has faster reads, but slower writes.
I'm just getting started with Subsonic 3.0 ActiveRecord and am trying to implement a batch query like the one in the SubSonic docs. I'm using a batch so I can query a User and a list of the users Orders in one shot.
When I call the BatchQuery.Queue() method, adding my "select user" query, SubSonic throws the following exception:
System.InvalidOperationException : Can't decide which property to consider the Key - you can create one called 'ID' or mark one with SubSonicPrimaryKey attribute
The code is as follows:
var db = new MyDB();
var userQuery = from u in db.Users //gets user by uid
where u.uid == 1
select u;
var provider = ProviderFactory.GetProvider();
var batch = new BatchQuery(provider);
batch.Queue(userQuery); //exception here
//create and add "select users orders" query here...
First things first - Why this error? My SubSonic Users object knows it's PK. "uid" is the PK in the database and the generated code reflects this. And I thought SubSonicPrimaryKey attribute was for the SimpleRepository? Is this way of batching not for ActiveRecord?
I could ask a number of other questions, but I'll leave it at that. If anyone can help me figure out what is going on and how to issue 2 batched queries I'd be grateful!
Edit - after further investigation
I ran through the source code with the debugger. Adam is correct - the ToSchemaTable() method in Objects.cs is apparently building out my schema and failing to find a PK. At the very end, it tries to find a column property named "ID" and flags this as the PK, otherwise it throws the exception. I added a check for "UID" and this works!
Still... I'm confused. I'm admittedly a bit lost after peeling back layer after layer of the source, but it seems like this portion of code is trying to build up a schema for my table and completely ignoring my generated User class - which quite nicely identifies which column/property is the PK! It doesn't seem quite right that I'd be required to name all keys "ID" w/ ActiveRecord.
I think the answer you're looking for is that this is a really stupid bug on my part. I'm hoping to push another build next week and if you could put this on the issue list I'd really appreciate it. My apologies...
SubSonic expects your primary key to be called Id so it's getting confused. SubSonicPrimaryKey is for simple repository but I assume where that exception is being thrown is shared between the different templates. If you rename your PK to Id or id or ID your query will work.