eager-loading

问题 I have a number of custom find_by_sql queries in Rails. I would like to use eager loading with them but there doesn't seem to be a good way to do this. I have seen the eager_custom.rb file floating around and it doesn't seem to work with Rails now. It appear Rails does eager loading differently now, using 2 queries (the regular query plus a query where the 'id IN' the ids from the first query), instead of the single join query used in the past. My question is if I do a custom SQL query, then

问题 I have a model with TPT inheritance. Location ( abstract ) Street ( derived from Location) GoogleStreetView ( 1 Street -> 0..1 GoogleStreetView ) Each of the above has it's own table. All was working fine until i added the "GoogleStreetView" table (which is backed by a PK/FK to Street). When i try and do this: var street = _locationRepository .Find() .OfType<Street>() .Include(x => x.GoogleStreetView) .SingleOrDefault(x => x.LocationId == 1); I get the error: The ResultType of the specified

问题 I've got a Hibernate object which's properties are all loaded lazy. Most of these properties are other Hibernate objects or PersistentSets. Now I want to force Hibernate to eager load these properties for just one time. Of course I could "touch" each of these properties with object.getSite().size() but maybe there's another way to achieve my goal. 回答1: The documentation puts it like this: You can force the usual eager fetching of properties using fetch all properties in HQL. References

问题 I have a database with four tables. TableA and TableB are the main tables and the TableC is the table of the many to many relationships. TableA(IDTableA, Name...) TableB(IDTableB, Name...) TableC(IDTableA, IDTableB) This create three entities, The EntityA has an ICollection of Entity C and Entity C has a Collection of EntitiesB, so when I try to get the related entities I do this: myContext.EntityA.Include(a=>a.EntityB.Select(b=>b.EntityC)); But this throw and exception that says that the

问题 I'm eager loading a model object with its associations: user= User.includes(:posts).find(1) But then at certain points in the code I would like to do something like this: user.posts.where(:topic => "x") But that just re-runs the query again. So instead I thought I'd do this: user.posts.select{|post| post.topic == "x" } That doesn't re-run the query. But I have a couple of questions. First, Is this the right way to do it? Second, I'm a bit confused about what select does in this case. Because

问题 As we all know that it is recommended to use annotations from javax.enterprise.context instead of javax.faces.bean as they are getting deprecated. And we all found ManagedBeans with eager="true" annotated with @ApplicationScoped from javax.faces.bean and having a @PostConstruct method are very useful to do web application initialization e.g: read properties from file system, initialize database connections, etc... Example : import javax.faces.bean.ApplicationScoped; import javax.faces.bean

问题 Background I have a rails application with deeply nested associations. .-< WorkPeriod Timecard -< Week -< Day -<--< Subtotal `-< Adjustment -< (has many) I'm using Active Model Serializer to build out the API. On the client side I want to load a timecard and all it's associations in one shot. Currently my serializers look like this, class TimecardSerializer < ActiveModel::Serializer embed :ids, include: true has_many :weeks end class WeekSerializer < ActiveModel::Serializer embed :ids,

问题 I'm trying to work out how to eager load the customers in the following HQL query: select order.Customer from Order as order where order.Id in ( select itemId from BadItem as badItem where (badItemType = :itemType) and (badItem.Date >= :yesterday) ) There's the usual many-to-one relationship between orders and customers. I'd like to do this is in the query, as opposed to the mapping, if possible - as in a "join fetch..." Maybe the query would be refactored as a join and I'm having a mental

问题 I want to load root entities and eager load all it's child collection and aggregate members. Have been trying to use the SetFetchMode in FluentNHibernate, but I am getting duplicates in one of the child collection since I have a depth of 3 levels. DistinctRootEntityResultTransformer unfortunately only removes the root duplications. return Session.CreateInvoiceBaseCriteria(query, archived) .AddOrder(new Order(query.Order, query.OrderType == OrderType.ASC)) .SetFetchMode("States", FetchMode

问题 For example I have a blog object, and that blog has many posts. I want to do eager loading of say the first blog object and include say the first 10 posts of it. Currently I would do @blogs = Blog.limit(4) and then in the view use @blogs.posts.limit(10) . I am pretty sure there is a better way to do this via an include such as Blog.include(:posts).limit(:posts=>10) . Is it just not possible to limit the number of included objects, or am I missing something basic here? 回答1: Looks like you can