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DAL 2 - Controlling your Mappings

I presented a session on the DAL 2 at DNN World in Orlando, and a few people asked about “calculated” properties - or properties that do not have any matching column in the database.  This is an important feature for any “auto-mapped” repository implementation, so we have added three new Attributes that control the mapping of properties and columns.

IgnoreColumn Attribute

The first of the new attributes is the IgnoreColumn attribute.  Applying this attribute to a property will mean that the property is ignored when mapping the class to it’s corresponding Database table.  Continuing to use the Task class from previous blog posts, lets look at an updated version where there is a new property that shouldn’t be saved to the Database.

Listing 1: The Task class


The new “PropertyNotInDatabase” property does not have a corresponding column in the database, and this would throw an error.  This can be made to work by adding the new IgnoreColumn attribute - see Listing 2.

Listing 2: Aplying the IgnoreColumn Attribute


DeclareColumns and IncludeColumn Attribute

An alternative approach is to work the other way - i.e. require the class to specify columns that map to fields in the database.  This would be the preferred approach if the class has less “included” columns than “excluded” columns.  Or maybe as a developer you feel that your intentions are clearer by explicitly including columns to be mapped.

The DeclareColumns attribute can be applied at the class level, and if applied only properties that have the IncludeColumn attribute applied will be mapped to the database table - see Listing 3

Listing 3: Applying the DeclareColumns and IncludeColumns Attributes


So this concludes this introductory series of articles on the new DAL 2.  Please continue to send your feedback as you use it in your module development, so we can continue to improve it.

This blog is cross-posted from my personal blog.


Tim McCurdy
I get what you're trying to do, but why didn't you just add support for the Attributes which already exist under the DataAnnotations? This way, if I already had Entities designed using Entity Framework, they would just translate right over to DNN without (or with only minor) changes.

I've developed mappers which were much better than PetaPoco or EF, so I guess I just keep using my own.
* They map from DataReaders, DataTable etc into POCOs and back again.
* They map to/from Stored Procs to DbCommands (using the DB Metadata if I choose).
* They map to base class properties, and support nested objects.

Why are we still reinventing things like this in 2015?
Tim McCurdy Tuesday, May 05, 2015 2:49 PM (link)

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