- Entity Framework Auto Generated Key Guid
- Entity Framework Auto Generate Key Download
- Entity Framework Primary Key Attribute
- Entity Framework Auto Generate Key Codes
Value generation patterns
In order to use the Entity Framework, you need to create an Entity Data Model. You can take advantage of the Visual Studio Entity Data Model Wizard to generate an Entity Data Model from a database automatically. Follow these steps: Right-click the Models folder in the Solution Explorer window and select the menu option Add, New Item. Data Annotations - Timestamp Attribute in EF 6 & EF Core. EF 6 and EF Core both include the Timestamp data annotation attribute. It can only be applied once in an entity class to a byte array type property. It creates a column with timestamp data type in the SQL Server database. Entity Framework API automatically uses this Timestamp column in. Entity Framework Core Auto Generated guid asp.net-core-2.1 c# entity-framework-core. English (en). The primary key value needs to be specified even if it's usually generated by the database. It will be used to detect data changes between migrations.
There are three value generation patterns that can be used for properties:
- No value generation
- Value generated on add
- Value generated on add or update
No value generation
- Sep 14, 2016 Entity Framework Core supports different key generation strategies like identity, Sequence and HiLo. In my previous post, I talked about using SQL Server Sequence with EF Core to Create Primary Key. Database sequences are cached, scalable.
- I created a table via entity framework code-first with a primary key set to auto increment, but now I want to remove that auto-incrementing from the column. I've tried doing that with both fluent API. Generate the migration with the Package Manager Console (add-migration.
No value generation means that you will always supply a valid value to be saved to the database. This valid value must be assigned to new entities before they are added to the context.
Value generated on add
Value generated on add means that a value is generated for new entities.
Depending on the database provider being used, values may be generated client side by EF or in the database. If the value is generated by the database, then EF may assign a temporary value when you add the entity to the context. This temporary value will then be replaced by the database generated value during SaveChanges().
If you add an entity to the context that has a value assigned to the property, then EF will attempt to insert that value rather than generating a new one. A property is considered to have a value assigned if it is not assigned the CLR default value (null for string, 0 for int, Guid.Empty for Guid, etc.). For more information, see Explicit values for generated properties.
Warning
How the value is generated for added entities will depend on the database provider being used. Database providers may automatically setup value generation for some property types, but others may require you to manually setup how the value is generated.
Entity Framework Auto Generated Key Guid
For example, when using SQL Server, values will be automatically generated for GUID properties (using the SQL Server sequential GUID algorithm). However, if you specify that a DateTime property is generated on add, then you must setup a way for the values to be generated. One way to do this, is to configure a default value of GETDATE(), see Default Values.
Value generated on add or update
Value generated on add or update means that a new value is generated every time the record is saved (insert or update).
Like value generated on add, if you specify a value for the property on a newly added instance of an entity, that value will be inserted rather than a value being generated. It is also possible to set an explicit value when updating. For more information, see Explicit values for generated properties.
Warning
How the value is generated for added and updated entities will depend on the database provider being used. Database providers may automatically setup value generation for some property types, while others will require you to manually setup how the value is generated.
For example, when using SQL Server, byte[] properties that are set as generated on add or update and marked as concurrency tokens, will be setup with the rowversion data type - so that values will be generated in the database. However, if you specify that a DateTime property is generated on add or update, then you must setup a way for the values to be generated. One way to do this, is to configure a default value of GETDATE() (see Default Values) to generate values for new rows. You could then use a database trigger to generate values during updates (such as the following example trigger).
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Value generated on add
By convention, non-composite primary keys of type short, int, long, or Guid are set up to have values generated for inserted entities, if a value isn't provided by the application. Your database provider typically takes care of the necessary configuration; for example, a numeric primary key in SQL Server is automatically set up to be an IDENTITY column.
You can configure any property to have its value generated for inserted entities as follows:
Warning
This just lets EF know that values are generated for added entities, it does not guarantee that EF will setup the actual mechanism to generate values. See Value generated on add section for more details.
Default values
On relational databases, a column can be configured with a default value; if a row is inserted without a value for that column, the default value will be used.
You can configure a default value on a property:
You can also specify a SQL fragment that is used to calculate the default value:
Specifying a default value will implicitly configure the property as value generated on add.
Value generated on add or update
Entity Framework Auto Generate Key Download
Warning
This just lets EF know that values are generated for added or updated entities, it does not guarantee that EF will setup the actual mechanism to generate values. See Value generated on add or update section for more details.
Computed columns
On some relational databases, a column can be configured to have its value computed in the database, typically with an expression referring to other columns:
Note
In some cases the column's value is computed every time it is fetched (sometimes called virtual columns), and in others it is computed on every update of the row and stored (sometimes called stored or persisted columns). This varies across database providers.
Entity Framework Primary Key Attribute
No value generation
Entity Framework Auto Generate Key Codes
Disabling value generation on a property is typically necessary if a convention configures it for value generation. For example, if you have a primary key of type int, it will be implicitly set configured as value generated on add; you can disable this via the following: