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This article mainly introduces "the method of ASP.NET Core using EF to create model". In the daily operation, I believe many people have doubts about the method of ASP.NET Core using EF to create model. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts of "ASP.NET Core uses EF to create models". Next, please follow the editor to study!

1. Indexes

Indexing is a common concept across multiple datastores. Although they may be implemented differently in the data store, they can also be used to look up more efficiently based on a column (or a set of columns).

1.1 Agreement

By convention, an index is created in each attribute (or set of attributes) used as a foreign key.

1.2 data annotations

You cannot create an index using data annotations.

1.3Fluent API

You can use the familiar API to specify the index of a single attribute. By default, the index is not unique.

Class MyContext: DbContext {public DbSet Blogs {get; set;} protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity () / / configuration index .HasIndex (b = > b.Url);}} public class Blog {public int BlogId {get; set;} public string Url {get; set;}}

You can also specify that the index should be unique, which means that no two entities can have the same value for a given attribute.

ModelBuilder.Entity () .HasIndex (b = > b.Url) .IsUnique

You can also specify indexes for multiple columns.

Class MyContext: DbContext {public DbSet People {get; set;} protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity () .HasIndex (p = > new {p.FirstName, p.LastName});}} public class Person {public int PersonId {get; set;} public string FirstName {get; set;} public string LastName {get; set;} 2. Spare key

The alternate key, as opposed to the primary key, is used as an alternate unique identifier for each entity instance. The alternate key can be used as the target of the relationship. When using a relational database, this maps to the concept of unique indexes / constraints on alternate key columns and one or more foreign key constraints that reference columns. The system usually introduces alternate keys for you when needed, and you don't have to configure them manually.

2.1 Agreement

By convention, the system will introduce an alternate key for you when identifying the attribute (not the primary key) and act as the target of the relationship.

Class MyContext: DbContext {public DbSet Blogs {get; set;} public DbSet Posts {get; set;} protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity () .HasOne (p = > p.Blog) .WithMany (b = > b.Posts) .HasForeignKey (p = > p.BlogUrl) .HasPrincipalKey (b = > b.Url);}} public class Blog {public int BlogId {get; set } public string Url {get; set;} public List Posts {get; set;}} public class Post {public int PostId {get; set;} public string Title {get; set;} public string Content {get; set;} / / alternate key public string BlogUrl {get; set;} public Blog Blog {get; set;} 2.2 data Notes

You cannot configure alternate keys using data annotations.

2.3Fluent API

You can use the familiar API to configure a single property as an alternate key.

Class MyContext: DbContext {public DbSet Cars {get; set;} protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity () / / is configured as an alternate key. HasAlternateKey (c = > c.LicensePlate);}} class Car {public int CarId {get; set;} public string LicensePlate {get; set;} public string Make {get; set;} public string Model {get; set }} you can also use the familiar API to configure multiple properties as alternate keys (called composite standby keys). Class MyContext: DbContext {public DbSet Cars {get; set;} protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity () / / configured as an alternate key. HasAlternateKey (c = > new {c.State, c.LicensePlate});}} class Car {public int CarId {get; set;} public string State {get; set;} public string LicensePlate {get; set;} public string Make {get; set } public string Model {get; set;}} 3. Inherit

Inheritance in the EF model is used to control how inheritance in entity classes is represented in the database.

3.1 Agreement

By convention, it is up to the database provider to determine how inheritance is represented in the database. Detailed instructions on how to use a relational database provider to handle this situation. If two or more inheritance types are explicitly included in the model, EF only sets inheritance. EF does not scan for base or derived types that are not included in the model. You can include types in the model by exposing DbSet for each type in the inheritance hierarchy.

Class MyContext: DbContext {public DbSet Blogs {get; set;} public DbSet RssBlogs {get; set;}} public class Blog {public int BlogId {get; set;} public string Url {get; set;}} public class RssBlog: Blog {public string RssUrl {get; set;}}

If you do not want to expose the DbSet of one or more entities in the hierarchy, you can use the well-known API to ensure that they are included in the model. If you do not rely on conventions, you can use HasBaseType to explicitly specify the base type.

Class MyContext: DbContext {public DbSet Blogs {get; set;} protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity (). HasBaseType ();} 4. Supported field

Supported fields allow EF to read and write fields instead of properties. This can be useful when you use encapsulation in a class to restrict data access or through application code, but without these restrictions, you should read or write values from the database.

4.1 Agreement

By convention, the following fields are found as supported fields for a given attribute (listed in order of priority). Fields are found only for attributes contained in the model.

Public class Blog {private string _ url; public int BlogId {get; set;} public string Url {get {return _ url;} set {_ url = value;}

When a supporting field is configured, EF writes directly to the field when the entity instance is materialized from the database instead of using the attribute repository. If EF needs to read or write values at other times, it uses attributes, if possible. For example, if EF needs to update the value of an attribute, it will use the property setter, if defined. If the property is read-only, it writes to the field.

4.2 data comments

Supported fields cannot be configured through data annotations.

4.3Fluent API

You can use the familiar API to configure the supported fields of the property.

Class MyContext: DbContext {public DbSet Blogs {get; set;} protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity () .Property (b = > b.Url) .HasField ("_ validatedUrl");} public class Blog {private string _ validatedUrl; public int BlogId {get; set;} public string Url {get {return _ validatedUrl }} public void SetUrl (string url) {using (var client = new HttpClient ()) {var response = client.GetAsync (url) .result; response.EnsureSuccessStatusCode ();} _ validatedUrl = url;}} 4.3.1 controls when fields are used

You can configure when EF uses fields or properties. For supported options, see PropertyAccessMode enumeration.

ModelBuilder.Entity () .property (b = > b.Url) .HasField ("_ validatedUrl") .UsePropertyAccessMode (PropertyAccessMode.Field); 4.3.2 Fields without attributes

You can also create a conceptual attribute in your model that does not have a corresponding CLR attribute in the entity class, but uses fields to store the data in the entity. This is different from the shadow property, where the data is stored in the change tracker. This method is usually used if the entity class uses a method to get or set a value. Can be found in Property (...) The name of the field specified for EF in API. If there is no property with the given name, EF looks for the field.

Class MyContext: DbContext {public DbSet Blogs {get; set;} protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity () .property ("_ validatedUrl");} public class Blog {private string _ validatedUrl; public int BlogId {get; set;} public string GetUrl () {return _ validatedUrl } public void SetUrl (string url) {using (var client = new HttpClient ()) {var response = client.GetAsync (url) .result; response.EnsureSuccessStatusCode ();} _ validatedUrl = url;}

You can also choose to specify a name for the property instead of the field name. Then, use this name when creating the model, and most notably, it will be used for the column names that are mapped to in the database.

Protected override void OnModelCreating (ModelBuilder modelBuilder) {modelBuilder.Entity () .property ("Url") .HasField ("_ validatedUrl");}

If there are no attributes in the entity class, you can use EF.Property (...) in the LINQ query. Method to reference properties that are conceptually part of the model.

Var blogs = db.blogs.OrderBy (b = > EF.Property (b, "Url")); at this point, the study of "ASP.NET Core's method of creating a model using EF" is over, hoping to solve everyone's doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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