I would like to write a single Breeze Entity Query that will return results that span across multiple entities that relate.
Here is an example of what I am trying to do:
The following returns Stages from Institution
var queryStages = breeze.EntityQuery
.from("institution")
.where("stages", "any", "qualifiedName", "==", 'QA');
and
The following returned Stage Config from Stages
var queryStageConfigs = breeze.EntityQuery
.from("stages")
.where("stageConfig", "any", "configValue", "==", 'Green');
How can I write a single Breeze Entity Query to do this all in one call.
I really want to be able write queries that go as deep as I want to go through my entities.
Thanks for any help!
I think you can accomplish this using a composite where clause. This deep drill into related entities is similar to the last example in the "conditions on related properties" section here.
var predicate = breeze.Predicate
.create("stages", "any", "qualifiedName", "==", 'QA')
.or("stages", "any", "stageConfig", "any", "configValue", "==", "Green");
var query = breeze.EntityQuery
.from("institution")
.where(predicate);
Related
A user can create groups
A group had to have created by a user
A user can belong to multiple groups
A group can have multiple users
I have something like the following:
Parse.Cloud.afterSave('Group', function(request) {
var creator = request.user;
var group = request.object;
var wasGroupCreated = group.existed;
if(wasGroupCreated) {
var hasCreatedRelation = creator.relation('hasCreated');
hasCreatedRelation.add(group);
var isAMemberOfRelation = creator.relation('isMemberOf');
isAMemberOfRelation.add(group);
creator.save();
}
});
Now when I GET user/me with include=isMemberOf,hasCreated, it returns me the user object but with the following:
hasCreated: {
__type: "Relation"
className: "Group"
},
isMemberOf: {
__type: "Relation"
className: "Group"
}
I'd like to have the group objects included in say, 'hasCreated' and 'isMemberOf' arrays. How do I pull that using the REST API?
More in general though, am I approaching this the right way? Thoughts? Help is much appreciated!
First off, existed is a function that returns true or false (in your case the wasGroupCreated variable is always going to be a reference to the function and will tis always evaluate to true). It probably isn't going to return what you expect anyway if you were using it correctly.
I think what you want is the isNew() function, though I would test if this works in the Parse.Cloud.afterSave() method as I haven't tried it there.
As for the second part of your question, you seem to want to use your Relations like Arrays. If you used an array instead (and the size was small enough), then you could just include the Group objects in the query (add include parameter set to isMemberOf for example in your REST query).
If you do want to stick to Relations, realise that you'll need to read up more in the documentation. In particular you'll need to query the Group object using a where expression that has a $relatedTo pointer for the user. To query in this manner, you will probably need a members property on the Group that is a relation to Users.
Something like this in your REST query might work (replace the objectId with the right User of course):
where={"$relatedTo":{"object":{"__type":"Pointer","className":"_User","objectId":"8TOXdXf3tz"},"key":"members"}}
I have a object Ob with several fields f1,..,fn (of different types).
Now a list of object is shown in a GridView and I need to implement the sorting method.
The real problem is:
how can I run
(from ob in Ob_list orderby ob.f1 ascending)
when the sorting field is represented by a string (i.e. "f1")?
Unfortunately I am not able to get it with the reflection (I am not able to do something like ob.GetType().GetField("f1"), this is not mapped into sql code).
I have several fields to possibly sort the rows, which is the best&fastest approach to this?
Thank you very much!
LINQ execution is deferred until you actually enumerate over the results or access the "count", etc. Because of this, you can build up your LINQ statement in stages.
The below code is done in C#, but I'm sure the equivalent is possible in VB.NET.
First setup your basic query:
var query = (from ob in Ob_list);
At this point, nothing has actually gone to the database due to deferred execution.
Next, conditionally add your order by components:
if (sortField == "f1")
{
query = query.OrderBy(o => o.f1);
}
else if (sortField == "f2")
{
query = query.OrderBy(o => o.f2);
}
else
{
//...
}
And finally, collect your results
foreach (var item in query)
{
// Process the item
}
I've found this question: How do I specify the Linq OrderBy argument dynamically?
I'm using Entity Framework, so the first answer did not solved my problem. The second one however, worked great!
Hope it helps!
Starting with a List of entities and needing all dependent entities through an association, is there a way to use the corresponding navigation-propertiy to load all child-entities with one db-round-trip? Ie. generate a single WHERE fkId IN (...) statement via navigation property?
More details
I've found these ways to load the children:
Keep the set of parent-entities as IQueriable<T>
Not good since the db will have to find the main set every time and join to get the requested data.
Put the parent-objects into an array or list, then get related data through navigation properties.
var children = parentArray.Select(p => p.Children).Distinct()
This is slow since it will generate a select for every main-entity.
Creates duplicate objects since each set of children is created independetly.
Put the foreign keys from the main entities into an array then filter the entire dependent-ObjectSet
var foreignKeyIds = parentArray.Select(p => p.Id).ToArray();
var children = Children.Where(d => foreignKeyIds.Contains(d.Id))
Linq then generates the desired "WHERE foreignKeyId IN (...)"-clause.
This is fast but only possible for 1:*-relations since linking-tables are mapped away.
Removes the readablity advantage of EF by using Ids after all
The navigation-properties of type EntityCollection<T> are not populated
Eager loading though the .Include()-methods, included for completeness (asking for lazy-loading)
Alledgedly joins everything included together and returns one giant flat result.
Have to decide up front which data to use
It there some way to get the simplicity of 2 with the performance of 3?
You could attach the parent object to your context and get the children when needed.
foreach (T parent in parents) {
_context.Attach(parent);
}
var children = parents.Select(p => p.Children);
Edit: for attaching multiple, just iterate.
I think finding a good answer is not possible or at least not worth the trouble. Instead a micro ORM like Dapper give the big benefit of removing the need to map between sql-columns and object-properties and does it without the need to create a model first. Also one simply writes the desired sql instead of understanding what linq to write to have it generated. IQueryable<T> will be missed though.
I hope someone can help with this please.
I am trying to query an OLAP Fact table with NHibernate, but am struggling to get it to work. Its seems a simple requirement but I just cant see what the problem could be.
I have a central Fact table with several Dimension tables, one of the Dimensions has a secondary Dimension.
So ERD is. Fact >---1 Factor_Dim >---1 Target_Dim
My NHibernate query is.
facts = session.CreateCriteria(typeof(Fact), "facts")
.CreateAlias("facts.FactorDimension", "factDim", JoinType.InnerJoin)
.CreateAlias("factDim.TargetDimension", "targetDim",JoinType.InnerJoin)
.Add(Restrictions.Eq("targetDim.TargetID", targetId))
.List();
The error is "The multi-part identifier "targetdim2_.TargetID" could not be bound.". The generated SQL does not have the Factor_DIM or Target_DIM tables in the From clause.
Are there any alternative techniques to get this query to work? Id like to stick to this style as opposed to CreateSQLQuery() if possible.
Please help. Thanks.
Linq or QueryOver will be your cleanest solutions. If you are determined to stay with ICriteria you probably would want to wrap each of your entities with a class with common crud methods, it also makes your code access common, so code corrections are done in one place, not over hundres of files or classes.
Theres plenty of projects at http://nhforge.org/wikis/general/open-source-project-ecosystem.aspx which can help you out. I know NhGen ( http://sourceforge.net/projects/nhgen/ ) creates a CRUD class for each entity based on the NHibernate.Burrows GenericDao class with a few CRUD methods. It takes care of all the aliases and joins so queries become as simple as
IMessageDao messageDao = new MessageDao();
// Get All
IList<IMessage> messageList1 dao.FindAll();
// Find using QueryByExample
IList<IMessage> messageList2 = dao.FindByExample(messageDetails, orderBy)).ToList();
// Find using a simple entity query
IList<IMessage> messageList3 = messageDao.Find( new [] { Restrictions.Le(MessageHelper.Columns.Date, dateLastChecked) } );
// Find using a join and a query on said joined entities
IList<IMessage> messageList4 = messageDao.Find
( new []
{
Restrictions.Le(MessageHelper.Columns.Date, dateLastChecked),
Restrictions.Eq(MessageHelper.Columns.IsActive, true))
}, new[]
{
Restrictions.Eq(CategoryHelper.KeyColumns.Rsn, categoryRsn),
Restrictions.Eq(CategoryHelper.Columns.IsActive, true))
}, new []
{
Restrictions.Eq(ChannelHelper.KeyColumns.Rsn, channelRsn),
Restrictions.Eq(ChannelHelper.Columns.IsActive, true))
}
);
Theres plenty of overrides so you can specify your join type or it naturally assumes inner join.
Im trying to return a SimpleQuery list that queries a single table and uses IN.
I can get this to work using
return new List<Jobs>(
ActiveRecordMediator<Jobs>.FindAll(Expression.In("ServiceId", ids))
);
However this is really really really slow. So id like to do something like this
SimpleQuery<Job> query =
new SimpleQuery<Job>(#"from Job as j where ? in (j.ServiceId)", ids);
return new List<Job>(query.Execute());
However I cant get the SimpleQuery to work. I cant find any documentation covering this and was hoping someone out there would be able to help.
Thanks
Have a look at the NHibernate HQL documentation here.
I'm guessing from your code, that you're after a HQL query to return all jobs where the job.ServiceID in a list of ids.
Maybe something along the lines,
IQuery q = s.CreateQuery("from Job as j where j.ServiceId in (:serviceIds)");
q.SetParameterList("serviceIds", ids);
BTW, have you heard of the NHibernate Lambda Extensions project?
Below is an example of the IN query done using the the mentioned library. Might be something interesting to look at as an alternative to using HQL.
DetachedCriteria after =
DetachedCriteria.For<Person>()
.Add(SqlExpression.In<Person>(p => p.Name,
new string[] { "name1", "name2", "name3" }));