lazy-loading

问题 Please read on before saying anything along the lines of "specify the fetch type in the query". That's not what I'm after. I'm looking for a way to eager-load a complete object-graph (the object + all its children and all their children and so on). I do not want to enumerate all properties that are to be loaded. I don't know them until runtime. N+1 queries aren't a problem. But at the end of this magical operation, I don't want a single proxy or lazy collection left in my graph. It should be

问题 I have a lookup table and a data table in my db. I'll use gender and person for an example. So let's say the gender table looks like so: Id Code 1 Male 2 Female and the person table looks like so: Id Name GenderId 1 Bob 1 2 Jane 2 I've modelled both tables in EF code first like so: public class Gender { public int Id {get;set;} public string Code {get;set;} } public class Person { public int Id {get;set;} public string Name {get;set;} public int GenderId {get;set;} public virtual Gender {get

问题 Interested in knowing how lazy loading is achieved in frameworks like Django. When is the decision made to perform the join? And is there a way to force eager loading in Django? Are there times when you would need to force Django to eager load? 回答1: The general answer is that Django makes the decision to perform the query when you actually ask for some records. Most commonly this means iterating over the queryset ( for record in queryset: ) or using the list() built-in function to convert the

问题 I have a WPF form with a TabControl containing 2 TabItems. I have validation occuring on controls on one tab that enforce dependent validation of controls on the other tab. However, when the user switches to the second tab, it does not show any the red square around the validated control because the tab contents aren't rendered until that TabItem is viewed for the first time. Is there a way to load the contents of all tabs when the Window is loaded? Update: I figured out a way to do this, but

问题 i use spring 3.2, spring data and jpa. i save an Advertisement object, after i save message i try to access message from Advertisement but it's null @Entity public class Advertisement implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO) private Long id; @OneToMany(mappedBy="id", cascade={CascadeType.REMOVE}, fetch=FetchType.LAZY) private Set<Message> messages; } @Entity public class Message implements Serializable { @Id @GeneratedValue(strategy = GenerationType.AUTO)

问题 I have an asp.net-mvc site and i am trying to understand the recommended practice around transactions and lazy loading. When doing research around implementating nhibernate second level cache, one rule of thumb is around wrapping everything in a transaction (see here and here). I am trying to reconcile this point with how lazy loading works because they seems to be at odds given deferred query execution. Lets say i have a query that looks like this . . I have two entities: Project Owner Here

问题 If I implement a Singleton either through holder idiom or double checked locking, but instead of calling 'getInstance()', use reflection to instantiate it, and then call 'getInstance()' on it, this would create two instances, breaking the pattern. So I add a static 'counter' member to the class, increment it in the class's private constructor, and throw an exception if it crosses '1'. But in that case, if I first instantiate through reflection, nobody else would be able to call 'getInstance()

问题 In many project which I take care of it there is nothing like lazy paging in datatables. Does JSF have some kind of magic or am I right that its really big performance problem. If you watch some tutorials almost no one take care of lazy paging Lets say you got List on backing bean and you have 2000 rows in DB. If I ll use ORM (JPA) when I want to display DataTable with this list from backing bean. JPA has to map 2000 objects this operation will take some times also allocate a lot of memory.

问题 I created an R shiny application that has a dygraph based on a data table that is dynamically subsetted by a checkboxGroupInput. My problem is, when I attempt to load large amounts of data (millions of records), it loads very slowly and/or crashes. After doing some more research, I stumbled upon a "lazy-load" technique from here. Based on my understanding, this technique essentially downsamples the data by only loading the number of data points equal to the width of the dygraph window. As the

问题 When writing CodeIgniter applications my controller actions tend to begin with a few lines as below: $this->load->model('abc_model'); $this->load->library('ijk'); And then (just for completeness) they're used as follows: $this->abc_model->fetch_123(); $this->ijk->do_something(); Would there be anything too wrong about extending MY_Controller so that the following was possible? $this->model('zbc_model')->fetch_stuff(); $this->library('ijk')->do_something(); Pros: Classes aren't loaded until