Methods and common problems using MySQL in EF_MySQL

Sometimes you need to rent space or database online. Mysql is cheaper, so you want to convert sql server to mysql...

Note: When installing Mysql, you must select the text set as utf8, otherwise you will not be able to use Chinese (currently you can also use utf8 when creating a database, but I don’t know how to set it up when EF generates a database, I hope an expert can give me some guidance)

1. Reference the EF package of mysql in the project

Install via NuGet package manager: EntityFramework6.1.3, MySql.Data.Entity6.9.8

You can also use the nuget command line to join:

Install-Package MySql.Data.Entity

2. Create new related classes

1. Create a new User entity class

And define the field length of the instance. If not defined, the error "Specified key was too long; max key length is 767 bytes" will appear. This is because the string type is longtext if it is directly mapped to mysql, and mysql supports a maximum length of 767 bytes.

public class User
{
public int Id { get; set; }
[StringLength(30)]
public string UserName { get; set; }
[MaxLength(30)]
public string PassWord { get; set; } } 

2. Create a new MyContext class

And explain how to use MySql to implement [DbConfigurationType(typeof(MySqlEFConfiguration))]

[DbConfigurationType(typeof(MySqlEFConfiguration))]
public class MyContext : DbContext
{
public MyContext()
: base("name=MyContext")//web.config中connectionstring的名字
{
}
public DbSet<User> Users { get; set; }
}

3. Write test code

Database.SetInitializer(new DropCreateDatabaseIfModelChanges<MyContext>());
var context = new MyContext();
//插入一行值
context.Users.Add(new User { UserName = "EF6MySQL" });
context.SaveChanges(); 

3. Configure Web.config

Add the following code to :

<add name="MyContext" connectionString="Data Source=localhost;port=3306;Initial Catalog=MySQL_EF;user id=root;password=root;" providerName="MySql.Data.MySqlClient" />

The complete web.config is as follows:

<?xml version="1.0" encoding="utf-8"?>




















<add name="MyContext" connectionString="Data Source=localhost;port=3306;Initial Catalog=MySQL_EF;user id=root;password=root;" providerName="MySql.Data.MySqlClient" />

 

Finally, run the program to complete the automatic creation of the database

FAQ

•An error message appears: Specified key was too long;max key length is 767 bytes

1) Check whether the string type attribute of the entity has a length set

2) Whether the MyContext class is declared to be generated as mysql data type [DbConfigurationType(typeof(MySqlEFConfiguration))]

•An error message appears: Model compatibility cannot be checked because the database does not contain model metadata

Delete the generated database and re-run the program

•An error message appears: The sequence does not contain any matching elements

Check it out:

For example: 1.

public class Employee
{
[Key]
public int EmployeeId { get; set; }
public string Name { get; set; }
[ForeignKey("ManagerId")]
public Employee Manager { get; set; }
public int ManagerId { get; set; }
}[ForeignKey("ManagerId")] public Employee Manager { get; set; } public int ManagerId { get; set; }这个外键设置。 

2.[Column(TypeName="VARCHAR(254)")] public string ColumnName { get; set; } Change this definition to: [MaxLength(254)] [Column(TypeName="VARCHAR")] public string ColumnName { get; set; }3. (The following code has not been tested because I do not use it this way. It will be tested in the next article)

modelBuilder.Entity<Category>()
.HasKey(c => c.IdCategory )
.HasOptional(p => p.Children)
.WithMany()
.HasForeignKey(c => c.ChildrenId);

changed to:

modelBuilder.Entity<Category>()
.HasKey(c => c.IdCategory )
.HasMany(p => p.Children)
.WithOptional()
.HasForeignKey(c => c.ChildrenId);

.WithMany() is replaced with .WithOptional()

The above is a complete description of the methods of using MySQL in EF and common problems introduced by the editor. I hope it will be helpful to you. If you have any questions, please leave me a message and the editor will reply to you in time. of. Thank you very much for your support of the website!