c# - Entity Framework Core 约定在哪里？

Question

使用 EF 6.1+ 时，我们有时需要添加或删除现有限制。代码看起来或多或少像:

public class MyContext : DbContext
    {
            protected override void OnModelCreating(DbModelBuilder modelBuilder)
            {
                modelBuilder.Conventions.AddFromAssembly(Assembly.GetExecutingAssembly());
                modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
                modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();
                modelBuilder.Conventions.Remove<ManyToManyCascadeDeleteConvention>();

                base.OnModelCreating(modelBuilder);
            }
}

如何在 EF 核心中做同样的事情？ Modelbuilder 没有 Conventions 属性 :(

Answer 1

我正在将一些代码从 EF 移植到 EF Core 2.1+，等不及 EF Core 3.0，所以写了一些扩展方法，这有点帮助..

public static IEnumerable<IMutableEntityType> EntityTypes(this ModelBuilder builder)
{
    return builder.Model.GetEntityTypes();
}

public static IEnumerable<IMutableProperty> Properties(this ModelBuilder builder)
{
    return builder.EntityTypes().SelectMany(entityType => entityType.GetProperties());
}

public static IEnumerable<IMutableProperty> Properties<T>(this ModelBuilder builder)
{
    return builder.EntityTypes().SelectMany(entityType => entityType.GetProperties().Where(x => x.ClrType == typeof(T)));
}

public static void Configure(this IEnumerable<IMutableEntityType> entityTypes, Action<IMutableEntityType> convention)
{
    foreach (var entityType in entityTypes)
    {
        convention(entityType);
    }
}

public static void Configure(this IEnumerable<IMutableProperty> propertyTypes, Action<IMutableProperty> convention)
{
    foreach (var propertyType in propertyTypes)
    {
        convention(propertyType);
    }
}

例如，您可以使用这些编写类似于 EF 6.1.x 中的约定。

// equivalent of modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
modelBuilder.EntityTypes()
            .Configure(et => et.Relational().TableName = et.DisplayName());

// Put the table name on the primary key
modelBuilder.Properties()
            .Where(x => x.Name == "Id")
            .Configure(p => p.Relational().ColumnName = p.DeclaringEntityType.Name + "Id");

// Mark timestamp columns as concurrency tokens
modelBuilder.Properties()
            .Where(x => x.Name == "Timestamp")
            .Configure(p => p.IsConcurrencyToken = true);

对于 EF Core 3.0，元模型方法略有变化，因此您需要

modelBuilder.EntityTypes()
            .Configure(et => et.SetTableName(et.DisplayName()));

modelBuilder.Properties()
            .Where(x => x.Name == "Id")
            .Configure(p => p.SetColumnName(BaseName(p.DeclaringEntityType.Name) + "Id"));

还没有检查这个效率但是除非你的模型很大它不应该造成问题

这可以通过外键、索引等其他助手进行扩展