未使用 Entity Framework Core 3.1（代码优先方法）在 MySql 数据库中创建用户表答案

【问题标题】：The User table is not created in MySql database using Entity Framework Core 3.1 (Code-first approach )未使用 Entity Framework Core 3.1（代码优先方法）在 MySql 数据库中创建用户表
【发布时间】：2020-08-29 02:24:47
【问题描述】：

如何使用 Code First 方法和 Entity Framework Core 3.1 在 MySql 数据库中创建用户表？

"DataAccessMySqlProvider": "server=localhost;database=jahan_alpha;uid=xxxx;password=xxxx" in appsettings.json

在 startup.cs 中：

public void ConfigureServices(IServiceCollection services)
{
   services.AddDbContext<ApplicationDbContext>(options =>
            options.UseMySQL(Configuration["ConnectionStrings:DataAccessMySqlProvider"],
            b => b.MigrationsAssembly("Alpha.DataAccess")));
   // .UseMySQL is in Microsoft.EntityFrameworkCore namespace
}

我在包管理器控制台中运行Add-Migration Init-MySql-database，然后运行Update-database。这样做之后，我得到了这个错误：

PM> Update-Database Build started... Build succeeded.
Microsoft.EntityFrameworkCore.Infrastructure[10403]
      Entity Framework Core 3.1.3 initialized 'ApplicationDbContext' using provider 'Pomelo.EntityFrameworkCore.MySql' with options:
MigrationsAssembly=Alpha.DataAccess 
Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (1,299ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      CREATE DATABASE `jahan_alpha`; Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (9,281ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      CREATE TABLE `__EFMigrationsHistory` (
          `MigrationId` varchar(95) NOT NULL,
          `ProductVersion` varchar(32) NOT NULL,
          CONSTRAINT `PK___EFMigrationsHistory` PRIMARY KEY (`MigrationId`)
      ); Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (118ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA='jahan_alpha' AND TABLE_NAME='__EFMigrationsHistory';
Microsoft.EntityFrameworkCore.Database.Command[20101]
      Executed DbCommand (5ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      SELECT `MigrationId`, `ProductVersion`
      FROM `__EFMigrationsHistory`
      ORDER BY `MigrationId`; Microsoft.EntityFrameworkCore.Migrations[20402]
      Applying migration '20200515231101_Init-MySql'. Applying migration '20200515231101_Init-MySql'. fail:
Microsoft.EntityFrameworkCore.Database.Command[20102]
      Failed executing DbCommand (181ms) [Parameters=[], CommandType='Text', CommandTimeout='30']
      ALTER TABLE `User` DROP INDEX `UserNameIndex`; Failed executing DbCommand (181ms) [Parameters=[], CommandType='Text',
CommandTimeout='30'] ALTER TABLE `User` DROP INDEX `UserNameIndex`;
MySql.Data.MySqlClient.MySqlException (0x80004005): Table
'jahan_alpha.user' doesn't exist  --->
MySql.Data.MySqlClient.MySqlException (0x80004005): Table
'jahan_alpha.user' doesn't exist
    at MySqlConnector.Core.ResultSet.ReadResultSetHeaderAsync(IOBehavior ioBehavior) in C:\projects\mysqlconnector\src\MySqlConnector\Core\ResultSet.cs:line 49
    at MySql.Data.MySqlClient.MySqlDataReader.ActivateResultSet() in C:\projects\mysqlconnector\src\MySqlConnector\MySql.Data.MySqlClient\MySqlDataReader.cs:line 130
    at MySql.Data.MySqlClient.MySqlDataReader.CreateAsync(CommandListPosition commandListPosition, ICommandPayloadCreator payloadCreator, IDictionary`2 cachedProcedures, IMySqlCommand command, CommandBehavior behavior, IOBehavior ioBehavior, CancellationToken cancellationToken) in C:\projects\mysqlconnector\src\MySqlConnector\MySql.Data.MySqlClient\MySqlDataReader.cs:line 391
    at MySqlConnector.Core.CommandExecutor.ExecuteReaderAsync(IReadOnlyList`1 commands, ICommandPayloadCreator payloadCreator, CommandBehavior behavior, IOBehavior ioBehavior, CancellationToken cancellationToken) in C:\projects\mysqlconnector\src\MySqlConnector\Core\CommandExecutor.cs:line 62
    at MySql.Data.MySqlClient.MySqlCommand.ExecuteNonQueryAsync(IOBehavior ioBehavior, CancellationToken cancellationToken) in C:\projects\mysqlconnector\src\MySqlConnector\MySql.Data.MySqlClient\MySqlCommand.cs:line 226
    at MySql.Data.MySqlClient.MySqlCommand.ExecuteNonQuery() in C:\projects\mysqlconnector\src\MySqlConnector\MySql.Data.MySqlClient\MySqlCommand.cs:line 74
    at Microsoft.EntityFrameworkCore.Storage.RelationalCommand.ExecuteNonQuery(RelationalCommandParameterObject parameterObject)
    at Microsoft.EntityFrameworkCore.Migrations.MigrationCommand.ExecuteNonQuery(IRelationalConnection connection, IReadOnlyDictionary`2 parameterValues)
    at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationCommandExecutor.ExecuteNonQuery(IEnumerable`1 migrationCommands, IRelationalConnection connection)
    at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.Migrate(String targetMigration)
    at Pomelo.EntityFrameworkCore.MySql.Migrations.Internal.MySqlMigrator.Migrate(String targetMigration)
    at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.UpdateDatabase(String targetMigration, String contextType)
    at Microsoft.EntityFrameworkCore.Design.OperationExecutor.UpdateDatabaseImpl(String targetMigration, String contextType)
    at Microsoft.EntityFrameworkCore.Design.OperationExecutor.UpdateDatabase.<>c__DisplayClass0_0.<.ctor>b__0()
    at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Table 'jahan_alpha.user' doesn't exist

ApplicationDbContext：

namespace Alpha.DataAccess
{
    public class ApplicationDbContext : IdentityDbContext<User, Role, int, UserClaim, UserRole, UserLogin, RoleClaim, UserToken>
    {
        public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options)
        {

        }
        // some codes...

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            // it should be placed here, otherwise it will rewrite the following settings!
            base.OnModelCreating(modelBuilder);

            modelBuilder.Entity<RoleClaim>(builder =>
            {
                builder.HasOne(roleClaim => roleClaim.Role).WithMany(role => role.Claims).HasForeignKey(roleClaim => roleClaim.RoleId);
                builder.ToTable("RoleClaim");
            });
            modelBuilder.Entity<Role>(builder =>
            {
                builder.ToTable("Role");
            });
            modelBuilder.Entity<UserClaim>(builder =>
            {
                builder.HasOne(userClaim => userClaim.User).WithMany(user => user.Claims).HasForeignKey(userClaim => userClaim.UserId);
                builder.ToTable("UserClaim");
            });
            modelBuilder.Entity<UserLogin>(builder =>
            {
                builder.HasOne(userLogin => userLogin.User).WithMany(user => user.Logins).HasForeignKey(userLogin => userLogin.UserId);
                builder.ToTable("UserLogin");
            });

            modelBuilder.Entity<User>(builder =>
            {
                builder.ToTable("User"); //.HasMany(e => e.Comments).WithOne().OnDelete(DeleteBehavior.Cascade);
            });
            modelBuilder.Entity<UserRole>(builder =>
            {
                builder.HasOne(userRole => userRole.Role).WithMany(role => role.Users).HasForeignKey(userRole => userRole.RoleId);
                builder.HasOne(userRole => userRole.User).WithMany(user => user.Roles).HasForeignKey(userRole => userRole.UserId);
                builder.ToTable("UserRole");
            });
            modelBuilder.Entity<UserToken>(builder =>
            {
                builder.HasOne(userToken => userToken.User).WithMany(user => user.UserTokens).HasForeignKey(userToken => userToken.UserId);
                builder.ToTable("UserToken");
            });

            // some codes...
        }

        public static async Task CreateAdminAccount(IServiceProvider serviceProvider, IConfiguration configuration)
        {
            UserManager<User> userManager = serviceProvider.GetRequiredService<UserManager<User>>();
            RoleManager<Role> roleManager = serviceProvider.GetRequiredService<RoleManager<Role>>();

            string userName = configuration["Data:AdminUser:Name"];
            string email = configuration["Data:AdminUser:Email"];
            string password = configuration["Data:AdminUser:Password"];
            string role = configuration["Data:AdminUser:Role"];

            if (await userManager.FindByNameAsync(userName) == null)
            {
                if (await roleManager.FindByNameAsync(role) == null)
                {
                    await roleManager.CreateAsync(new Role(role));
                }

                User user = new User
                {
                    Email = email,
                    UserName = userName
                };
                var result = userManager.CreateAsync(user, password);
                if (result.IsCompletedSuccessfully)
                {
                    await userManager.AddToRoleAsync(user, role);
                }
            }
        }
    }
}

【问题讨论】：

不需要提前创建一个空数据库。1.尝试删除现有数据库并删除所有迁移文件。2.然后运行命令add-migraion init和update-database。如果仍然包含此类错误。请分享您的模型和 DbContext。
我更新了问题。

标签： asp.net-core entity-framework-core ef-code-first mysql-workbench asp.net-core-3.1

【解决方案1】：

基于执行的第一个命令是 ALTER DATABASE 的事实，我假设 1) 当您生成初始迁移时，您已经有一个手动生成的数据库，其中包含表 User，并且 2) 然后您删除了数据库 3 ) 然后你运行Update-Database 命令。

将迁移视为将数据库从一种稳定状态转移到另一种稳定状态的增量补丁。如果您想查看更新数据库时将运行的实际 SQL，可以发出 dotnet ef migrations script -i -o migrations.sql 命令。这将生成一个完整的脚本，其中包含从初始状态到当前状态的所有迁移。

我进一步假设您实际上在隐藏的// some codes... 代码块中的ApplicationDbContext 中有一个DbSet<User> 属性

正如在 cmets 中已经指出的，你需要做的是；

从服务器localhost 删除jahan_alpha 数据库
从您的项目中完全删除 Migrations 文件夹
运行dotnet ef migrations add initial
运行dotnet ef migrations script -i -o migrations.sql
验证migrations.sql 文件中的SQL 命令是否正确（例如CREATE DATABASE 在ALTER DATABASE 的任何实例之前）
现在运行dotnet ef database update - 这将使用您的代码优先项目中定义的架构生成jahan_alpha 数据库

【讨论】：