1.) change type of ID to int instead of string. 2.) not recommended!!! - handle autoincrement by yourself. You first need to get the latest value from the database, parse it to the integer, increment it and attach it to the entity as a string again. This article exlains how to create an Entity Key in the Entity Framework. The DetailTable entity has a composite primary key on DetailId and MasterId. Using the preceding two described methods we can generate an Entity Key of any entity object and using the Entity Key we can retrieve the entire entity from the object context. Jun 20, 2014 Hi why auto increment (identity) does not work in Entity Framework 6.1.0.0? I use this code for auto increment Id in my Users Table: public class User DatabaseGenerated(DatabaseGeneratedOption.I.
A key serves as a unique identifier for each entity instance. Most entities in EF have a single key, which maps to the concept of a primary key in relational databases (for entities without keys, see Keyless entities). Entities can have additional keys beyond the primary key (see Alternate Keys for more information).
By convention, a property named
Id or <type name>Id https://brownflight683.weebly.com/blog/sso-generate-private-key-net-c. will be configured as the primary key of an entity.
Note
Owned entity types use different rules to define keys.
You can configure a single property to be the primary key of an entity as follows: https://brownflight683.weebly.com/blog/windows-7-ultimate-activation-key-generator.
You can also configure multiple properties to be the key of an entity - this is known as a composite key. Composite keys can only be configured using the Fluent API; conventions will never setup a composite key, and you can not use Data Annotations to configure one.
Primary key name
By convention, on relational databases primary keys are created with the name
PK_<type name> . You can configure the name of the primary key constraint as follows:
Key types and values
While EF Core supports using properties of any primitive type as the primary key, including
string , Guid , byte[] and others, not all databases support all types as keys. In some cases the key values can be converted to a supported type automatically, otherwise the conversion should be specified manually.
Key properties must always have a non-default value when adding a new entity to the context, but some types will be generated by the database. In that case EF will try to generate a temporary value when the entity is added for tracking purposes. After SaveChanges is called the temporary value will be replaced by the value generated by the database.
Chevy blazer chilton manual download. Important
If a key property has its value generated by the database and a non-default value is specified when an entity is added, then EF will assume that the entity already exists in the database and will try to update it instead of inserting a new one. To avoid this turn off value generation or see how to specify explicit values for generated properties.
Alternate Keys
An alternate key serves as an alternate unique identifier for each entity instance in addition to the primary key; it can be used as the target of a relationship. When using a relational database this maps to the concept of a unique index/constraint on the alternate key column(s) and one or more foreign key constraints that reference the column(s).
Tip
If you just want to enforce uniqueness on a column, define a unique index rather than an alternate key (see Indexes). In EF, alternate keys are read-only and provide additional semantics over unique indexes because they can be used as the target of a foreign key.
Alternate keys are typically introduced for you when needed and you do not need to manually configure them. By convention, an alternate key is introduced for you when you identify a property which isn't the primary key as the target of a relationship.
You can also configure a single property to be an alternate key:
You can also configure multiple properties to be an alternate key (known as a composite alternate key):
Finally, by convention, the index and constraint that are introduced for an alternate key will be named -->
AK_<type name>_<property name> (for composite alternate keys <property name> becomes an underscore separated list of property names). You can configure the name of the alternate key's index and unique constraint:
When working with Entity Framework Code First the default behavior is to map your POCO classes to tables using a set of conventions baked into EF. Sometimes, however, you cannot or do not want to follow those conventions and need to map entities to something other than what the conventions dictate.
There are two main ways you can configure EF to use something other than conventions, namely annotations or EFs fluent API. The annotations only cover a subset of the fluent API functionality, so there are mapping scenarios that cannot be achieved using annotations. This article is designed to demonstrate how to use the fluent API to configure properties.
The code first fluent API is most commonly accessed by overriding the OnModelCreating method on your derived DbContext. The following samples are designed to show how to do various tasks with the fluent api and allow you to copy the code out and customize it to suit your model, if you wish to see the model that they can be used with as-is then it is provided at the end of this article.
Model-Wide SettingsDefault Schema (EF6 onwards)
Starting with EF6 you can use the HasDefaultSchema method on DbModelBuilder to specify the database schema to use for all tables, stored procedures, etc. This default setting will be overridden for any objects that you explicitly configure a different schema for.
Custom Conventions (EF6 onwards)
Starting with EF6 you can create your own conventions to supplement the ones included in Code First. For more details, see Custom Code First Conventions.
Property Mapping
The Property method is used to configure attributes for each property belonging to an entity or complex type. The Property method is used to obtain a configuration object for a given property. The options on the configuration object are specific to the type being configured; IsUnicode is available only on string properties for example.
Configuring a Primary Key
The Entity Framework convention for primary keys is:
To explicitly set a property to be a primary key, you can use the HasKey method. In the following example, the HasKey method is used to configure the InstructorID primary key on the OfficeAssignment type.
Configuring a Composite Primary Key
The following example configures the DepartmentID and Name properties to be the composite primary key of the Department type. For mac.
Switching off Identity for Numeric Primary Keys
Ssh with private key. The following example sets the DepartmentID property to System.ComponentModel.DataAnnotations.DatabaseGeneratedOption.None to indicate that the value will not be generated by the database.
Specifying the Maximum Length on a Property
In the following example, the Name property should be no longer than 50 characters. If you make the value longer than 50 characters, you will get a DbEntityValidationException exception. If Code First creates a database from this model it will also set the maximum length of the Name column to 50 characters.
Configuring the Property to be Required
In the following example, the Name property is required. If you do not specify the Name, you will get a DbEntityValidationException exception. If Code First creates a database from this model then the column used to store this property will usually be non-nullable.
Note
In some cases it may not be possible for the column in the database to be non-nullable even though the property is required. For example, when using a TPH inheritance strategy data for multiple types is stored in a single table. If a derived type includes a required property the column cannot be made non-nullable since not all types in the hierarchy will have this property.
Configuring an Index on one or more properties
Note
EF6.1 Onwards Only - The Index attribute was introduced in Entity Framework 6.1. If you are using an earlier version the information in this section does not apply.
Creating indexes isn't natively supported by the Fluent API, but you can make use of the support for IndexAttribute via the Fluent API. Index attributes are processed by including a model annotation on the model that is then turned into an Index in the database later in the pipeline. You can manually add these same annotations using the Fluent API.
The easiest way to do this is to create an instance of IndexAttribute that contains all the settings for the new index. You can then create an instance of IndexAnnotation which is an EF specific type that will convert the IndexAttribute settings into a model annotation that can be stored on the EF model. https://brownflight683.weebly.com/blog/the-crew-key-generator-free-download. These can then be passed to the HasColumnAnnotation method on the Fluent API, specifying the name Index for the annotation.
For a complete list of the settings available in IndexAttribute, see the Index section of Code First Data Annotations. This includes customizing the index name, creating unique indexes, and creating multi-column indexes.
You can specify multiple index annotations on a single property by passing an array of IndexAttribute to the constructor of IndexAnnotation.
Specifying Not to Map a CLR Property to a Column in the Database
The following example shows how to specify that a property on a CLR type is not mapped to a column in the database.
Mapping a CLR Property to a Specific Column in the Database
The following example maps the Name CLR property to the DepartmentName database column.
Renaming a Foreign Key That Is Not Defined in the Model
If you choose not to define a foreign key on a CLR type, but want to specify what name it should have in the database, do the following:
Configuring whether a String Property Supports Unicode Content
By default strings are Unicode (nvarchar in SQL Server). You can use the IsUnicode method to specify that a string should be of varchar type.
Configuring the Data Type of a Database Column
The HasColumnType method enables mapping to different representations of the same basic type. https://namesite302.weebly.com/offline-thesaurus-download-for-android.html. Using this method does not enable you to perform any conversion of the data at run time. https://zcsphei.weebly.com/download-applications-for-mac.html. Note that IsUnicode is the preferred way of setting columns to varchar, as it is database agnostic.
Configuring Properties on a Complex Type
There are two ways to configure scalar properties on a complex type.
You can call Property on ComplexTypeConfiguration.
You can also use the dot notation to access a property of a complex type.
Configuring a Property to Be Used as an Optimistic Concurrency Token
To specify that a property in an entity represents a concurrency token, you can use either the ConcurrencyCheck attribute or the IsConcurrencyToken method.
You can also use the IsRowVersion method to configure the property to be a row version in the database. Setting the property to be a row version automatically configures it to be an optimistic concurrency token.
Type MappingEntity Framework Set Primary KeySpecifying That a Class Is a Complex Type
By convention, a type that has no primary key specified is treated as a complex type. There are some scenarios where Code First will not detect a complex type (for example, if you do have a property called ID, but you do not mean for it to be a primary key). In such cases, you would use the fluent API to explicitly specify that a type is a complex type.
Specifying Not to Map a CLR Entity Type to a Table in the Database
The following example shows how to exclude a CLR type from being mapped to a table in the database.
Mapping an Entity Type to a Specific Table in the Database
All properties of Department will be mapped to columns in a table called t_ Department.
You can also specify the schema name like this:
Entity Framework Generate Primary Key ExamplesMapping the Table-Per-Hierarchy (TPH) Inheritance
In the TPH mapping scenario, all types in an inheritance hierarchy are mapped to a single table. A discriminator column is used to identify the type of each row. When creating your model with Code First, TPH is the default strategy for the types that participate in the inheritance hierarchy. By default, the discriminator column is added to the table with the name “Discriminator” and the CLR type name of each type in the hierarchy is used for the discriminator values. You can modify the default behavior by using the fluent API.
Mapping the Table-Per-Type (TPT) InheritanceEntity Framework Id Primary Key
In the TPT mapping scenario, all types are mapped to individual tables. Properties that belong solely to a base type or derived type are stored in a table that maps to that type. Tables that map to derived types also store a foreign key that joins the derived table with the base table.
Mapping the Table-Per-Concrete Class (TPC) Inheritance
In the TPC mapping scenario, all non-abstract types in the hierarchy are mapped to individual tables. The tables that map to the derived classes have no relationship to the table that maps to the base class in the database. All properties of a class, including inherited properties, are mapped to columns of the corresponding table.
Call the MapInheritedProperties method to configure each derived type. MapInheritedProperties remaps all properties that were inherited from the base class to new columns in the table for the derived class.
Note
Note that because the tables participating in TPC inheritance hierarchy do not share a primary key there will be duplicate entity keys when inserting in tables that are mapped to subclasses if you have database generated values with the same identity seed. To solve this problem you can either specify a different initial seed value for each table or switch off identity on the primary key property. Identity is the default value for integer key properties when working with Code First.
Mapping Properties of an Entity Type to Multiple Tables in the Database (Entity Splitting)
Entity splitting allows the properties of an entity type to be spread across multiple tables. In the following example, the Department entity is split into two tables: Department and DepartmentDetails. Entity splitting uses multiple calls to the Map method to map a subset of properties to a specific table.
Mapping Multiple Entity Types to One Table in the Database (Table Splitting)
The following example maps two entity types that share a primary key to one table.
Mapping an Entity Type to Insert/Update/Delete Stored Procedures (EF6 onwards)
Starting with EF6 you can map an entity to use stored procedures for insert update and delete. For more details see, Code First Insert/Update/Delete Stored Procedures.
Model Used in Samples
The following Code First model is used for the samples on this page.
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