Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <blockquote> <p>"I would like to add attributes to a Django models programmatically. At class creation time"</p> </blockquote> <p>Don't. "Programmatically" adding columns is silly and confusing. It seems fine to you -- the developer -- who deeply gets the nuances of Django.</p> <p>For us, the maintainers, that code will (a) make no sense and (b) have to be replaced with simple, obvious code that does the same job the simplest most obvious way.</p> <p>Remember, the maintainers are violent sociopaths who know where you live. Pander to them with simple and obvious code.</p> <p>There's no reason to replace a cluster of simple attribute definitions with a tricky-looking loop. There's no improvement and no savings.</p> <ol> <li><p>The run-time performance of the view functions is the same.</p></li> <li><p>The one-time class-definition has saved a few lines of code that are executed once during application start-up. </p></li> <li><p>The development cost (i.e., solving this question) is higher.</p></li> <li><p>The maintenance cost (i.e., turning this code over to someone else to keep it running) is astronomically high. The code will simply be replaced with something simpler and more obvious.</p></li> </ol> <p>Even if you have 100's of currencies, this is still a perfectly bad idea.</p> <blockquote> <p>"I don't want a related model for these prices"</p> </blockquote> <p>Why not? A related model is (1) simple, (2) obvious, (3) standard, (4) extensible. It has almost no measurable cost at run time or development time and certainly no complexity.</p> <blockquote> <p>"For instance, lets say I have a Car model class and want to add one price attribute (database column) per currency, given a list of currencies."</p> </blockquote> <p>That is <em>not</em> a new attribute at all.</p> <p>That is a new value (in a row) of a table that has Car Model and Currency as the keys.</p> <p>You class looks something like this:</p> <pre><code>class Price( models.Model ): car = models.ForeignKey( Car ) currency = models.ForeignKey( Currency ) amount = models.DecimalField() </code></pre> <p>Previous Version of the question</p> <blockquote> <p>"I would like to add attributes to a Django models programmatically, at run time."</p> </blockquote> <p>Don't. There are absolutely no circumstances under which you ever want to add attributes to a database "at run time".</p>
    singulars
    1. This table or related slice is empty.
    1. POProgrammatically specifying Django model attributes
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USS.Lott
    1. USS.Lott
    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. 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. COWhy the cocky attitude? I understand your view here completely. But in this case, I wanted the currencies as columns in the database - not as a related model. Using a separate model (and database table) introduces a SQL join that's simply not OK in this case where there is a fixed set of currencies that changes really seldom (like about once a year or so). Adding a second level of abstraction is nice, but also introduces overhead both in terms of performance and complexity.
      singulars
      1. PO
      1. USmojbro
    2. COI agree my choice of words here, "at run time", is not the best. But I completely disagree on your opinion that there are absolutely no circumstances where you'd like to programmatically alter the model definitions.
      singulars
      1. PO
      1. USmojbro
    3. CO@mojbro: You're missing the point. The point is not one of performance. It's a matter of definition. When using the relational model, there is absolutely no reason to try to add columns at run time. If you want to change your question, I can change my answer. But the relational model was very carefully designed to make adding attributes at run time completely unnecessary. Any attempt to add attributes at run time means, one overlooked a relational design pattern.
      singulars
      1. PO
      1. USS.Lott
 

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