IT:AD:Code First:DataAnnotations [Notes]

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# IT:AD:Code First:DataAnnotations #



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## Summary ##

>Important: the use of `DataAnnotations` is not recommended in anything but a POC.

* Domain Entities should be in their own assembly.
* Decorating domain [[IT/#Entities/]] with Attributes drag in -- and therefore to all assemblies referring to domain entities (ie everywhere) -- creates brittle cod e(see: [[IT/AD/Patterns/Vendors Suck Strategy/]]).
* Prefer the fluent approach: [[IT/AD/Code First/FluentAPI/]]
    * Not only do they not cause dependencies, but the Fluent approach offers more options.


## Attributes ##

That said, the most common EF Attributes one can apply are:

* `[Key]` – Column(s) that define the Primary Key in the database table
* `[StringLength]` – Minimal and maximal string length (only used for validation purposes not as database constraints)
* `[MaxLength]` – Can be used instead of `[StringLength]` to just define the maximal string length of a column
* `[ConcurrencyCheck]` – Flag that indicates that concurrency checks are activated for the column 
* `[Required]` – Flag that indicates that a value is required for the column (column is flagged as not null)
* `[Timestamp]` – Flag on time stamp columns which is used for concurrency checks
* `[Column]` – Specify the name of a column (default property name), can also be used to define the column position
* `[Table]` – Specify the name of a table (default class name)
* `[DatabaseGenerated]` – Flag that indicates that the value is filled by the database (possible values are Computed, Identity, None)
* `[NotMapped]` – Is used to define a property in the class that does not get generated in the database.
* `[ForeignKey]` and `[InverseProperty]` – Column(s) that are defined as Foreign Keys



## Resources ##


* [[IT/AD/Data/Annotations/]]

* [Override DisplayName](http://stackoverflow.com/questions/356464/localization-of-displaynameattribute)
* [Relationship between DisplayName and Display](http://www.dotnetcurry.com/ShowArticle.aspx?ID=715)

* http://msdn.microsoft.com/en-us/library/system.data.entity.modelconfiguration.conventions(v=vs.103).aspx