Entity Framework Code-First（9）：DataAnnotations

DataAnnotations in Code-First:

EF Code-First provides a set of DataAnnotation attributes, which you can apply to your domain classes and properties. DataAnnotation attributes override default Code-First conventions.System.ComponentModel.DataAnnotations includes attributes that impacts on nullability or size of the column. System.ComponentModel.DataAnnotations.Schema namespace includes attributes that impacts the schema of the database.

Note: DataAnnotations only give you a subset of configuration options. Fluent API provides a full set of configuration options available in Code-First.

System.ComponentModel.DataAnnotations Attributes:

Attribute	Description
Key	Mark property as EntityKey which will be mapped to PK of the related table.
Timestamp	Mark the property as a non-nullable timestamp column in the database.
ConcurrencyCheck	ConcurrencyCheck annotation allows you to flag one or more properties to be used for concurrency checking in the database when a user edits or deletes an entity.
Required	The Required annotation will force EF (and MVC) to ensure that property has data in it.
MinLength	MinLength annotation validates property whether it has minimum length of array or string.
MaxLength	MaxLength annotation is the maximum length of property which in turn sets the maximum length of a column in the database
StringLength	Specifies the minimum and maximum length of characters that are allowed in a data field.

System.ComponentModel.DataAnnotations.Schema Attributes:

Attribute	Description
Table	Specify name of the DB table which will be mapped with the class
Column	Specify column name and datatype which will be mapped with the property
Index	Create an Index for specified column. (EF 6.1 onwards only)
ForeignKey	Specify Foreign key property for Navigation property
NotMapped	Specify that property will not be mapped with database
DatabaseGenerated	DatabaseGenerated attribute specifies that property will be mapped to computed column of the database table. So, the property will be read-only property. It can also be used to map the property to identity column (auto incremental column).
InverseProperty	InverseProperty is useful when you have multiple relationships between two classes.
ComplexType	Mark the class as complex type in EF.

Learn about each DataAnnotation attributes in the next sections.