Facets (CSDL)

Artykuł
08/29/2011

Facets in conceptual schema definition language (CSDL) represent constraints on properties of entity types and complex types. Facets appear as XML attributes on the following CSDL elements:

The following table describes the facets that are supported in CSDL. All facets are optional. Some facets listed below are used by the Entity Framework when generating a database from a conceptual model. For more information, see Generate Database Wizard.

Note

For information about data types in a conceptual model, see Conceptual Model Types (CSDL).

Facet	Description	Applies to	Used for the database generation	Used by the runtime
Collation	Specifies the collating sequence (or sorting sequence) to be used when performing comparison and ordering operations on values of the property.	Edm.String	Yes	No
ConcurrencyMode	Indicates that the value of the property should be used for optimistic concurrency checks.	All EDMSimpleType properties	No	Yes
Default	Specifies the default value of the property if no value is supplied upon instantiation.	All EDMSimpleType properties	Yes	Yes
FixedLength	Specifies whether the length of the property value can vary.	Edm.Binary, Edm.String	Yes	No
MaxLength	Specifies the maximum length of the property value.	Edm.Binary, Edm.String	Yes	No
Nullable	Specifies whether the property can have a null value.	All EDMSimpleType properties	Yes	Yes
Precision	For properties of type Decimal, specifies the number of digits a property value can have. For properties of type Time, DateTime, and DateTimeOffset, specifies the number of digits for the fractional part of seconds of the property value.	Edm.DateTime, Edm.DateTimeOffset, Edm.Decimal, and Edm.Time.	Yes	No
Scale	Specifies the number of digits to the right of the decimal point for the property value.	Edm.Decimal	Yes	No
Unicode	Indicates whether the property value is stored as Unicode.	Edm.String	Yes	Yes

Note When generating a database from a conceptual model, the Generate Database Wizard will recognize the value of the StoreGeneratedPattern attribute on a Property element if it is in the following namespace: https://schemas.microsoft.com/ado/2009/02/edm/annotation. The supported values for the attribute are Identity and Computed. A value of Identity will produce a database column with an identity value that is generated in the database. A value of Computed will produce a column with a value that is computed in the database.

Example

The following example shows facets applied to the properties of an entity type:

<EntityType Name="Product">
  <Key>
    <PropertyRef Name="ProductId" />
  </Key>
  <Property Type="Int32" 
            Name="ProductId" Nullable="false" 
            a:StoreGeneratedPattern="Identity" 
   xmlns:a="https://schemas.microsoft.com/ado/2009/02/edm/annotation" />
  <Property Type="String" 
            Name="ProductName" 
            Nullable="false" 
            MaxLength="50" />
  <Property Type="String" 
            Name="Location" 
            Nullable="true" 
            MaxLength="25" />
</EntityType>

For more information, see Property Element (CSDL).

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Facets (CSDL)

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