Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <blockquote> <p>Basically, the first update should win and the second should fail.</p> <p>Does it suffice to add a version to the Member class</p> </blockquote> <p>Yes, it does. Say you and I read an entity from the database with version = x. I make some changes to property1 of the entity and commit to the database. Now the entity in the database has version = x+1. Now, you change property2 of your version of the entity (property1 still holds the older value). When you update the changed entity to the database, the changes made by me to property1 would be lost as you would overwrite it with the old value. But this will not happen as Hibernate would check from any changes that might have occurred between the time of reading the entity and updating it. When you go to update the entity Hibernate sees that the version of the entity in the database is different from the version of entity that you have provided. This means that someone else has made some changes to the object i.e. the object that you have supplied is stale and hence a StaleStateException is thrown.</p> <blockquote> <p>However, say that there is a gender field, I would like to be able to update the gender field without caring if the location is being updated by another transaction.</p> </blockquote> <p>This is not possible using hibernate (it should be clear from the above example). If this was supported, then changes made to the location would be lost when and update made to the gender is committed containing the older value of location. Some degree of tolerance can be achieved using some logic and explicit version checking and updating the changed fields before updating the entity, but the problem still exists, you can never know at what moment the changes will be made to the object. In my opinion, such an implementation will be an overkill with not enough benefit.</p>
    singulars
    1. This table or related slice is empty.
    1. POHibernate: update field in entity only if specific field is null
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USSatadru Biswas
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. COThanks for the info. I guess then now, moving away from hibernate, I only want to give location a value only if it is currently null, allowing for concurrency. However, I don't want to block on each call to setLocation, rather, I want to block on calls to setLocation for a particular member id, so that two calls to setLocation for two different members don't block, but two calls to setLocation for the same member do block. I haven't found a good way to do this that I like: http://stackoverflow.com/questions/659915/synchronizing-on-an-integer-value
      singulars
      1. PO
      1. USjsl
    2. COWould it suffice to use a stored procedure that checks for the member, if he does not exist, return -1, otherwise if the member does exist and he has a location, return 0 (don't update), otherwise update the location and return 1. Would the database properly handle concurrent calls to the stored procedure?
      singulars
      1. PO
      1. USjsl
    3. CO@jsl You should check out pessimistic locking in Hibernate. This would allow only one thread to make changes to the entity at a time, blocking others who want to make changes to the same entity. However this will also block threads who want to update some property other than location
      singulars
      1. PO
      1. USSatadru Biswas
 

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