entity framework annotations
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entity framework annotations
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entity framework annotations
You may choose to put a connection string in your app.config file. You want combo of PageID and SortOrder to be unique. It is up to the provider or data store to validate as appropriate. more Prime Library. The general idea of a Seed Method is to initialize data into a database that is being created by Code First or evolved by Migrations. In Entity Framework 6, the DbModelBuilder class acts as a Fluent API using which we can configure many different things. To fix these problems, you can use the InverseProperty annotation to specify the alignment of the properties. Store data that is short-lived and could be easily deleted by simply deleting the table. The Property method is used to configure attributes for each property belonging to an entity or complex type. Lets take a look at the following code in which Index attribute is added in Course class for Credits. The Student, Course and Enrollment classes follow this convention. Below are the Student and Enrollment which has one-to-many relationship, but the foreign key in Enrollment table is not following the default Code First conventions. To configure one-to-zero or one relationship between Student and StudentLogIn using Fluent API, you need to override OnModelCreating method as shown in the following code. This data is often test data, but may also be reference data such as lists of known Students, Courses, etc. You can only have one timestamp property in a given class. protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity() .Property(p => p.LastName) .IsConcurrencyToken(); } Timestamp/rowversion A timestamp/rowversion is a property for which a new value is automatically generated by the database every time a row is inserted or updated. All these we discussed in data annotations and here we will see how to achieve the same things using Fluent API. In Model First, you define your model in an Entity Framework designer then generate SQL, which will create database schema to match your model and then you execute the SQL to create the schema in your database. In Model First, you define your model in an Entity Framework designer then generate SQL, which will create database schema to match your model and then you execute the SQL to create the schema in your database. EF6, because we cannot set it on the property itself but instead on the class. You cannot only specify the table name but you can also specify a schema for the table using Table attribute as shown in the following code. Lets take a look at the following example where we will add another class into our model to create a one-to-one relationship. However, there is no StudentID property in the Student class, but it is StdntID property is Student class. It is up to the provider or data store to validate if appropriate. If you're using a relational database, entity properties map to table columns. Entity Framework is no longer tied or dependent to the .NET release cycle. An entity set is a collection of instances of a specific entity type. Configures the primary key property(s) for this entity type. Following are the main types of mapping which Fluent API supports . If a local SQL Express instance is available then Code First has created the database on that instance. Since Entity Framework Core (EF Core) 5.0 we can configure Unique Indexes via Data Annotations.. (Inherited from StructuralTypeConfiguration), Configures a struct property that is defined on this type. Required attribute will force EF to ensure that the property has data in it. As a result, the StudentCourses table is created with Course_CourseID and Student_ID columns as shown in the following image. Similarly, youll also need to add in the Course class referenced by these properties. Full-text fields are broken down into tokens and normalized (lowercased, ). Fluent API uses the Modelbuilder instance to configure the domain model. Each association end also specifies an association end multiplicity that indicates the number of entities that can be at that end of the association. Indexing is the new feature in Entity Framework where you can improve the performance of your Code First application by reducing the time required to query data from the database. Connection string name must start with "name=" otherwise, it will consider it as a database name. This feature was introduced in EF Core 6.0. Now, Code First will include Title column in update command to check for optimistic concurrency as shown in the following code. Type in the following command to add the Entity Framework to the project. You can configure a column as non-Unicode as follows: The Data Annotation for configuring Unicode was introduced in EF Core 6.0. An ethnic group or an ethnicity is a grouping of people who identify with each other on the basis of shared attributes that distinguish them from other groups. Go back to the terminal window that should still be open in the EFSample folder. In all versions of Entity Framework, whenever you execute SaveChanges() to insert, update or delete the database, the framework will wrap that operation in a transaction. Step 7 Choose Entity Framework 6.x and click Next. If you are letting Code First create the database, and also want to change the name of the columns in your tables. EF Core is a complete rewrite and contains many new features not available in EF6, although it also still lacks some of the most advanced mapping capabilities of EF6. For example, in the above diagram Student and Enrollment tables have one-tomany relationship, each student may have many enrollments, but each enrollment belongs to only one student. We also published the 7.0 preview 1 release of the Microsoft.Data.Sqlite provider for ADO.NET.. Following is the implementation on MyContext class, which is derived from DbContext class. A property is considered optional if it is valid for it to contain null. The MaxLength attribute allows you to specify additional property validations. If that's not the case you can specify the name of the column with the Column attribute as shown in the following code. A Course entity can be related to any number of Enrollment entities. Student domain class (entity) would map to the Students table. You want combo of PageID and SortOrder to be unique. Indexes make the retrieval of data faster and efficient, in most cases. + 's' EF will create a DB table with the entity class name suffixed by 's' e.g. Lets define a very simple model using classes. For example, a Student entity type may have properties such as Student Id, Name etc. If you are using an earlier version, the information in this section does not apply. Entity Framework is a Microsoft tool. The default Code First conventions are used to create a join table when database is generated. The following example introduces a unique index as shown in the following code. An entity represents a specific object such as a specific Student or Enrollment. Old behavior. Here, you will learn about code-based migration. You can see that NotMapped attribute is applied to the FatherName property. The question mark after the Grade type declaration indicates that the Grade property is nullable. We can get the reference to the ModelBuilder, when we override the onmodelcreating method of the DbContext.The ModelBuilder has several methods, which you can use to configure the model. Learn more, Learn ASP.Net MVC and Entity Framework (Database First), Learn Entity Framework Core 2.0 (EFC2) using ASP.Net Core, Entity Framework : A Comprehensive Course. A grade that's null is different from a zero grade. By using this website, you agree with our Cookies Policy. Lets take a look at a simple example by adding the TimeStamp property to the Course class . are configured as required, and all properties with nullable .NET value types (int?, decimal?, bool?, etc.) For example, the following code configures Url as a non-unicode string with maximum length of 200 and Rating as decimal with precision of 5 and scale of 2: Configuring a maximum length provides a hint to the database provider about the appropriate column data type to choose for a given property. @Configuration: Tags the class as a source of bean definitions for the application context. For DateTime properties, precision defines the maximum number of digits needed to express fractions of seconds, and scale is not used. Maybe try in the constructor this.Active = true;?I think the DB value will take precedence when fetching, but careful if new'ing then attaching an entity for an update without a fetch first, as the change tracking might see this as you wanting to update the value. When the table is generated, you will see IX_Credits in Indexes. General information about EF Core support for collations can be found in the collation documentation page. Enter BloggingContext as the name and click OK Lets take a look at the following example in which admin schema is applied. Data annotations and the fluent API can be used together, but Code First gives precedence to Fluent API > data annotations > default conventions. In the above code, snippet of context class connection string is specified as a parameter in the base constructor. protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity() .Property(p => p.LastName) .IsConcurrencyToken(); } Timestamp/rowversion A timestamp/rowversion is a property for which a new value is automatically generated by the database every time a row is inserted or updated. This is a key feature of the Entity Framework. Then . Which data types support precision and scale is database-dependent, but in most databases decimal and DateTime types do support these facets. There's a huge variety of mappings and modeling that you can impact using the configurations. Entity types contain properties that define their structure and characteristics. Code First will treat Timestamp properties the same as ConcurrencyCheck properties, but it will also ensure that the database field that code first generates is non-nullable. You can use stored procedures to perform predefined logic on database tables, and many organizations have policies in place that require the use of these stored procedures. Fluent API Configurations in EF 6. Lets take a look at a simple example in which we will rename the column name in student table from FirstMidName to FirstName as shown in the following code. Now, let us use the Fluent API to configure the one to one relationship. When you have composite keys, Entity Framework requires you to define an order of the key properties. For instance: Page object has a child collection of Elements. For example, SQL Server maps DateTime properties to datetime2(7) columns, and string properties to nvarchar(max) columns (or to nvarchar(450) for properties that are used as a key). Fluent API Configurations in EF 6. You can, however, specify a different column order: The Fluent API can be used to override ordering made with attributes, including resolving any conflicts when attributes on different properties specify the same order number. An Enrollment entity is associated with one Student and one Course entity, so the property can only hold a single Student and Course entity. For example, the following code snippet configures a SQL Server column to be case-insensitive: If all columns in a database need to use a certain collation, define the collation at the database level instead. You can create an index on one or more columns using the IndexAttribute. A University database can be much more complex as a whole but for demo and learning purpose, we are using the simplest form of this database. For instance: Page object has a child collection of Elements. The general idea of a Seed Method is to initialize data into a database that is being created by Code First or evolved by Migrations. Before ASP.NET Core 3.0, when you added a package reference to Microsoft.AspNetCore.App or Microsoft.AspNetCore.All, it would include EF Core and some of the EF Core data providers like the SQL Server provider. System.ComponentModel.DataAnnotations includes the following attributes that impacts the nullability or size of the column. Each primary key value relates to only one record (or no records) in the related table. Default Code First convention creates a table name similar to the class name. If run your application, then the database with MyContextDB name will be created in your local SQL server. Data Annotations Database Generated EF6 - Code First from Database! Column attribute overrides the default convention. It is the main class and on which you can configure all your domain classes. No foreign key property. You will see that Entity model and POCO classes are generated from the database. If you want to specify the join table name and the names of the columns in the table you need to do additional configuration by using the Map method.
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