Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>The observers aren't actually coupled to the class they are observing. The connection between the observer's handler and the observed object is made using literal string values (e.g. `upload.error'), which means that:</p> <ol> <li>If you want to observe a specific object, you have to know from beforehand the names of the events it will publishing; this is the "coupling" that you don't like.</li> <li>On the other hand, if you are interested in a specific event only, you can observe <em>any</em> type of object for that event without having any knowledge about that object.</li> </ol> <p>Item 2 above is a benefit that you care about, but what to do about item 1?</p> <p>If you think about it, there needs to be some way to differentiate between callbacks to the same observer if they represent different events taking place. These "identifiers", no matter what form they take, need to be packaged either into the observed object or be a part of the observer library code.</p> <p>In the first instance (inside observed object) you would probably need a way for observers to query "do you ever publish event X?" before starting to observe a target for that event. The target can answer this question just fine. This leaves a bitter taste of coupling, but if you want any object to observe any other, and you have no idea <em>what</em> you will be observing beforehand, I don't think you can do any better.</p> <p>In the second approach, you would have a number of well-known events defined (as <code>const</code> inside a class?) in your library. Presumably such a list of events can be made because the library tackles a concrete application domain, and that domain offers obvious choices for the events. Then, classes both internal to your library (which would end up being observed) and external to it (the observers which plug into the framework) would use these identifiers to differentiate between events. Many callback-based APIs (such as Win32) use an approach practically identical to this.</p>
    singulars
    1. This table or related slice is empty.
    1. POHow to implement a full Observer pattern in PHP
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USJon
    1. USJon
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POHow to implement a full Observer pattern in PHP
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COI just found the Symfony [Event Dispatcher](http://components.symfony-project.org/event-dispatcher/trunk/book/01-Event-Dispatcher) library and I think they handled it just like you said.
      singulars
      1. PO
      1. USXeoncross
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload