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Property Uniqueness? |
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jradxl 
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Joined: 14-Jun-2011 Posts: 30 |
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 Topic: Property Uniqueness?Posted: 10-Sep-2012 at 8:53am |
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Hi,
If a property needs to be unique (such as UserName or EmailAddress) but not a primary key how does one go about adding it in Code First? Is there an Attribute? OK, the UI can inforce it, but is there a Devforce database compatible way? thanks John |
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kimj
IdeaBlade 
Joined: 09-May-2007 Posts: 1391 |
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Posted: 10-Sep-2012 at 10:52am |
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DevForce is relying on the EF Code First attributes (or Fluent API) to define the model, and right now EF does not support unique keys. There are a couple of options though.
To add a unique constraint or index to the database table you can write a custom DbInitializer and create the index within the Seed method logic, or as of EF 4.3 use Db migrations. Here's some more information from StackOverflow - http://stackoverflow.com/questions/4413084/unique-constraint-in-entity-framework-code-first and http://stackoverflow.com/questions/8262590/entity-framework-code-first-fluent-api-adding-indexes-to-columns. You can also write a custom DevForce verifier to validate the property when it's set or the entity is saved - http://drc.ideablade.com/xwiki/bin/view/Documentation/validation-create-custom-verifier.
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mgood
IdeaBlade
Joined: 18-Nov-2010 Location: Emeryville, CA Posts: 583 |
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Posted: 10-Sep-2012 at 1:15pm |
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John,
Checking uniqueness takes a little bit more thought than simply putting a uniquness constraint on the property, unless you are perfectly happy with an exception if you are trying to save a duplicate. If that's the case, then stop reading. If you however want to alert the user before it hits the database, then read on.
Checking if a property is unique requires querying the DB. In Silverlight that is an asynchronous operation. In WPF it should be an asynchronous operation if you want a good performing application. The proper approach is a validation service that the ViewModel can asynchronously call before saving the data. There's still the possiblity that you get a constraint violation in the DB if an other user snuck in a save between you checking for uniquness and saving the data, so you should still have a DB constraint.
You can find more information and an example here:
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jradxl
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Joined: 14-Jun-2011 Posts: 30 |
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Posted: 10-Sep-2012 at 2:14pm |
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Thank you both for your quick and full responses.
Informing the User and a responsive application is indeed my goal, and so this is very useful. Indeed async operation in a WPF app was not something I had immediately thought of. Thanks John |
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