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I am trying to figure out what the
[DatabaseGenerated(DatabaseGenerationOption.Computed)]
DataAnnotation actually does. However, I cannot find any information via google searches or MSDN searches. Does anyone have any idea?
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The DatabaseGenerated attribute specifies how values are generated for a property by the database. The attribute takes a DatabaseGeneratedOption enumeration value, which can be one of three values: Computed. Identity. None.
An identity column in a database (and DatabaseGeneratedOption. Identity ) denote that the column generates the value automatically upon insert. These are typically int columns, and similar, that auto-increment. An INSERT for a row that uses an identity column omit a value from the query (generated by the database)
Advertisements. DataAnnotations is used to configure the classes which will highlight the most commonly needed configurations. DataAnnotations are also understood by a number of .
The Entity Framework Core Fluent API HasComputedColumnSql method is used to specify that the property should map to a computed column. The method takes a string indicating the expression used to generate the default value for a database column.
A computed column is a column on a table that is not updatable, but is instead based on other data in the row.
It is a similar concept to a View, but is more light-weight, and can be PERSISTED without having to build an indexed view.
For example, you could have a computed column to add together two numbers like this (in T-SQL):
CREATE TABLE [Foo]
(
[FooId] int NOT NULL IDENTITY,
CONSTRAINT [Foo_PK] PRIMARY KEY ([FooId]),
[ItemA] int,
[ItemB] int,
[Sum] AS ([ItemA] + [ItemB])
)
Entity Framework needs to know about these columns so that it doesn't try to issue an Update statement that would try to change the value of that column.
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