Sep 14, 2016 And EF Core supports “HiLo” out of the box. So in this post, we will see how to use HiLo to generate keys with Entity Framework Core. Use HiLo to generate keys with Entity Framework Core. To begin with, a little info about HiLo Pattern. HiLo is a pattern where the primary key is made of 2 parts “Hi” and “Lo”. @Tymek, erm, either way you have to hit the database to determine which Id should be next. But, if you let the database to handle it for you, you simply pass other parameters to the db and db figures out the value for you during handling the insert.If you handle the autoincrementing by yourself, you have to get the latest id from the database BEFORE you actually send a query to insert a record. Simple substitution cipher generate modified alphabet key python.
-->- The Entity Framework Core Fluent API ValueGeneratedOnAdd method indicates that the value for the selected property is generated by the database whenever a new entity is added to the database. Therefore, the property should be ignored by EF Core when constructing an INSERT statement.
- Generate Context and Entity Classes from an Existing Database in EF 6 Code-First Approach. Here, you will learn how to generate context and entity classes for an existing database, using the code-first approach. Entity Framework provides an easy way to use the code-first approach for an existing database.
- Nov 25, 2015 Auto-generated Guid in Entity Framework Code First When you create an entity in Code First model, you might need a Guid field. In addition you might want SQL Server should auto-generate values for that field.
- Sep 13, 2016 But the good news is, Entity Framework Core supports Sequence out of the box. I also mentioned in my earlier post Quick summary of what’s new in Entity Framework Core 1.0. So in this post, let’s find out how to use SQL Server Sequence in Entity Framework Core to create primary key. Use SQL Server Sequence in Entity Framework Core.
Value generation patterns
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
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.
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).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:
![Auto Auto](/uploads/1/2/5/8/125872183/428971880.png)
Entity Framework Auto Generate Key Download
Specifying a default value will implicitly configure the property as value generated on add.
Value generated on add or update
Warning
Entity Framework Key Order
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.
No value generation
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: