EF Core：不为各数据库单独创建IEntityTypeConfiguration类的替代方案

我为每个实体单独提取了IEntityTypeConfiguration<>配置类，有时需要针对不同数据库类型使用不同配置。例如：

PostgreSQL配置：

public class PostConfigurationPostgres : IEntityTypeConfiguration<Post>
{
    public void Configure(EntityTypeBuilder<Post> builder)
    {
        builder.Property(p => p.Created)
            .HasDefaultValueSql("now()");
    }
}

SQL Server配置：

public class PostConfigurationSqlServer : IEntityTypeConfiguration<Post>
{
    public void Configure(EntityTypeBuilder<Post> builder)
    {
        builder.Property(p => p.Created)
            .HasDefaultValueSql("getdate()");
    }
}

我的DbContext代码：

public class KnowDbContext : DbContext
{
    public KnowDbContext(DbContextOptions<KnowDbContext> options)
        : base(options){}
    public DbSet<Post>? Posts { get; set; }
    
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        var provider = this.Database.ProviderName;
        if (provider == "Npgsql.EntityFrameworkCore.PostgreSQL")
            modelBuilder.ApplyConfigurationsFromAssembly(typeof(KnowDbContext).Assembly,
                t => t.Name.Contains("Postgres"));
        else if (provider == "Microsoft.EntityFrameworkCore.SqlServer")
            modelBuilder.ApplyConfigurationsFromAssembly(typeof(KnowDbContext).Assembly,
                t => t.Name.Contains("SqlServer"));
    }
}

请问是否存在无需为每种数据库创建PostConfigurationSqlServer、PostConfigurationPostgres这类IEntityTypeConfiguration<>实现类的多数据库模型配置替代方案？

方案1：单配置类内判断数据库提供程序 #

把数据库特定配置逻辑合并到同一个IEntityTypeConfiguration实现类中，通过模型获取当前数据库提供程序后分支处理：

public class PostConfiguration : IEntityTypeConfiguration<Post>
{
    public void Configure(EntityTypeBuilder<Post> builder)
    {
        // 通用配置写在这里
        builder.HasKey(p => p.Id);

        // 数据库专属配置
        var provider = builder.Metadata.Model.GetDatabaseProvider();
        if (provider == "Npgsql.EntityFrameworkCore.PostgreSQL")
        {
            builder.Property(p => p.Created)
                .HasDefaultValueSql("now()");
        }
        else if (provider == "Microsoft.EntityFrameworkCore.SqlServer")
        {
            builder.Property(p => p.Created)
                .HasDefaultValueSql("getdate()");
        }
    }
}

对应的DbContext简化为：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.ApplyConfigurationsFromAssembly(typeof(KnowDbContext).Assembly);
}

方案2：封装数据库专属扩展方法 #

把重复的数据库判断逻辑封装成扩展方法，在配置类中直接调用，减少冗余代码：

public static class EntityTypeBuilderExtensions
{
    public static PropertyBuilder<DateTime> HasDefaultCreationDate(this PropertyBuilder<DateTime> builder, string providerName)
    {
        return providerName switch
        {
            "Npgsql.EntityFrameworkCore.PostgreSQL" => builder.HasDefaultValueSql("now()"),
            "Microsoft.EntityFrameworkCore.SqlServer" => builder.HasDefaultValueSql("getdate()"),
            _ => builder
        };
    }
}

配置类中使用：

public class PostConfiguration : IEntityTypeConfiguration<Post>
{
    public void Configure(EntityTypeBuilder<Post> builder)
    {
        var provider = builder.Metadata.Model.GetDatabaseProvider();
        builder.Property(p => p.Created)
            .HasDefaultCreationDate(provider);
    }
}

方案3：全局模型拦截器统一配置 #

如果有大量实体需要统一的数据库特定规则，可以用EF Core的模型拦截器全局处理：

public class DatabaseSpecificConfigurationInterceptor : IMutableModelInterceptor
{
    public void OnModelCreating(ModelCreatingEventData eventData, InterceptionResult result)
    {
        var model = eventData.Model;
        var provider = model.GetDatabaseProvider();

        // 遍历所有实体，对名为Created的DateTime字段统一配置默认值
        foreach (var entityType in model.GetEntityTypes())
        {
            var createdProperty = entityType.FindProperty("Created");
            if (createdProperty != null && createdProperty.ClrType == typeof(DateTime))
            {
                if (provider == "Npgsql.EntityFrameworkCore.PostgreSQL")
                {
                    createdProperty.SetDefaultValueSql("now()");
                }
                else if (provider == "Microsoft.EntityFrameworkCore.SqlServer")
                {
                    createdProperty.SetDefaultValueSql("getdate()");
                }
            }
        }
    }
}

在DbContext中注册拦截器：

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
    optionsBuilder.AddInterceptors(new DatabaseSpecificConfigurationInterceptor());
}

内容的提问来源于stack exchange，提问作者athene