使用Entity Framework Core 3.1在MySql数据库中没有创建User表（代码优先的方法）。

Question

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

而在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
}

我运行 Add-Migration Init-MySql-database 然后 Update-database 在Package Manager Console.做完之后，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);
                }
            }
        }
    }
}

Answer 1

基于第一个执行的命令是 ALTER DATABASE我假设：1)你已经有一个手动生成的数据库，其中有一个表是 User 当你生成初始迁移和2)然后你删除数据库3)然后你运行了 Update-Database 命令。

把迁移看成是把数据库从一个稳定状态移动到另一个稳定状态的增量补丁。如果你想看看更新数据库时实际运行的SQL，你可以发出 dotnet ef migrations script -i -o migrations.sql 命令，这将生成一个完整的脚本，包括从初始状态到当前状态的所有迁移。这将生成一个完整的脚本，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有一个 DbSet<User> 贵地 ApplicationDbContext 隐隐约约 // some codes... 码组

正如评论中已经指出的，你需要做的是。

• 删除 jahan_alpha 数据库 localhost
• 去掉 Migrations 完全从您的项目中的文件夹
• 运行 dotnet ef migrations add initial
• 运行 dotnet ef migrations script -i -o migrations.sql
• 中的SQL命令。migrations.sql 文件是正确的（例如 CREATE DATABASE 前的任何实例 ALTER DATABASE)
• 现行 dotnet ef database update - 这将产生 jahan_alpha 数据库，并在您的第一个项目中定义了模式。