如何使用Entity Framework自动过滤掉软删除的实体？

Question

我正在使用Entity Framework Code First.我重写SaveChanges的DbContext,让我做一个"软删除":

if (item.State == EntityState.Deleted && typeof(ISoftDelete).IsAssignableFrom(type))
{
    item.State = EntityState.Modified;
    item.Entity.GetType().GetMethod("Delete")
        .Invoke(item.Entity, null);

    continue;
}

这很好,所以对象知道如何将自己标记为软删除(在这种情况下它只是设置IsDeleted为true).

我的问题是我怎样才能使它在检索对象时忽略任何对象IsDeleted？所以,如果我说_db.Users.FirstOrDefault(UserId == id)如果该用户拥有IsDeleted == true它将忽略它.基本上我想过滤？

注意:我不想只是把&& IsDeleted == true 那就是为什么我用界面标记类,所以删除知道如何"正常工作",我想以某种方式修改检索,知道如何"正常工作"也基于那个界面存在.

Answer 1

我已经为我的所有实体进行了软删除工作,并且使用此答案建议的技术无法通过上下文检索软删除的项目.这包括您通过导航属性访问实体时.

将IsDeleted鉴别器添加到可以软删除的每个实体.不幸的是,我没有根据从抽象类或接口派生的实体(EF映射当前不支持接口作为实体)来解决如何执行此操作的问题:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
   modelBuilder.Entity<Foo>().Map(m => m.Requires("IsDeleted").HasValue(false));
   modelBuilder.Entity<Bar>().Map(m => m.Requires("IsDeleted").HasValue(false));

   //It's more complicated if you have derived entities. 
   //Here 'Block' derives from 'Property'
   modelBuilder.Entity<Property>()
            .Map<Property>(m =>
            {
                m.Requires("Discriminator").HasValue("Property");
                m.Requires("IsDeleted").HasValue(false);
            })
            .Map<Block>(m =>
            {
                m.Requires("Discriminator").HasValue("Block");
                m.Requires("IsDeleted").HasValue(false);
            });
}

覆盖SaveChanges并查找要删除的所有条目:

编辑 覆盖删除sql的另一种方法是更改EF6生成的存储过程

public override int SaveChanges()
{
   foreach (var entry in ChangeTracker.Entries()
             .Where(p => p.State == EntityState.Deleted 
             && p.Entity is ModelBase))//I do have a base class for entities with a single 
                                       //"ID" property - all my entities derive from this, 
                                       //but you could use ISoftDelete here
    SoftDelete(entry);

    return base.SaveChanges();
}

SoftDelete方法直接在数据库上运行sql,因为鉴别器列不能包含在实体中:

private void SoftDelete(DbEntityEntry entry)
{
    var e = entry.Entity as ModelBase;
    string tableName = GetTableName(e.GetType());
    Database.ExecuteSqlCommand(
             String.Format("UPDATE {0} SET IsDeleted = 1 WHERE ID = @id", tableName)
             , new SqlParameter("id", e.ID));

    //Marking it Unchanged prevents the hard delete
    //entry.State = EntityState.Unchanged;
    //So does setting it to Detached:
    //And that is what EF does when it deletes an item
    //http://msdn.microsoft.com/en-us/data/jj592676.aspx
    entry.State = EntityState.Detached;
}

GetTableName返回要为实体更新的表.它处理表链接到BaseType而不是派生类型的情况.我怀疑我应该检查整个继承层次结构....但是有计划改进Metadata API,如果我不得不考虑类型和表之间的EF Code First Mapping

private readonly static Dictionary<Type, EntitySetBase> _mappingCache 
       = new Dictionary<Type, EntitySetBase>();

private ObjectContext _ObjectContext
{
    get { return (this as IObjectContextAdapter).ObjectContext; }
}

private EntitySetBase GetEntitySet(Type type)
{
    type = GetObjectType(type);

    if (_mappingCache.ContainsKey(type))
        return _mappingCache[type];

    string baseTypeName = type.BaseType.Name;
    string typeName = type.Name;

    ObjectContext octx = _ObjectContext;
    var es = octx.MetadataWorkspace
                    .GetItemCollection(DataSpace.SSpace)
                    .GetItems<EntityContainer>()
                    .SelectMany(c => c.BaseEntitySets
                                    .Where(e => e.Name == typeName 
                                    || e.Name == baseTypeName))
                    .FirstOrDefault();

    if (es == null)
        throw new ArgumentException("Entity type not found in GetEntitySet", typeName);

    _mappingCache.Add(type, es);

    return es;
}

internal String GetTableName(Type type)
{
    EntitySetBase es = GetEntitySet(type);

    //if you are using EF6
    return String.Format("[{0}].[{1}]", es.Schema, es.Table);

    //if you have a version prior to EF6
    //return string.Format( "[{0}].[{1}]", 
    //        es.MetadataProperties["Schema"].Value, 
    //        es.MetadataProperties["Table"].Value );
}

我之前在迁移中使用自然键创建了索引,代码如下所示:

public override void Up()
{
    CreateIndex("dbo.Organisations", "Name", unique: true, name: "IX_NaturalKey");
}

但这意味着您无法创建与已删除组织同名的新组织.为了允许这个,我改变了代码来创建索引:

public override void Up()
{
    Sql(String.Format("CREATE UNIQUE INDEX {0} ON dbo.Organisations(Name) WHERE IsDeleted = 0", "IX_NaturalKey"));
}

这会从索引中排除已删除的项目

注意 如果相关项目被软删除,则不会填充导航属性,但外键是.例如:

if(foo.BarID != null)  //trying to avoid a database call
   string name = foo.Bar.Name; //will fail because BarID is not null but Bar is

//but this works
if(foo.Bar != null) //a database call because there is a foreign key
   string name = foo.Bar.Name;

PS投票进行全局过滤https://entityframework.codeplex.com/workitem/945?FocusElement=CommentTextBox#并过滤此处包括

Answer 2

使用EntityFramework.DynamicFilters.它允许您创建全局过滤器,这些过滤器将在执行查询时自动应用(包括针对导航属性).

项目页面上有一个示例"IsDeleted"过滤器,如下所示:

modelBuilder.Filter("IsDeleted", (ISoftDelete d) => d.IsDeleted, false);

该过滤器将针对ISoftDelete实体的任何查询自动注入where子句.过滤器在DbContext.OnModelCreating()中定义.

免责声明:我是作者.

Answer 3

一种选择是将其封装!IsDeleted到扩展方法中.下面的内容只是一个例子.请注意它只是为了让你了解一个扩展方法,下面将不会编译.

public static class EnumerableExtensions
{
    public static T FirstOrDefaultExcludingDeletes<T>(this IEnumerable<T> source, Func<T, bool> predicate)
    {
        return source.Where(args => args != IsDeleted).FirstOrDefault(predicate);
    }
}

用法:

_db.Users.FirstOrDefaultExcludingDeletes(UserId == id)

Answer 4

您可以在 Entity Framework Core 2.0 上使用全局查询过滤器。

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entity<Blog>().Property<string>("TenantId").HasField("_tenantId");

    // Configure entity filters
    modelBuilder.Entity<Blog>().HasQueryFilter(b => EF.Property<string>(b, "TenantId") == _tenantId);
    modelBuilder.Entity<Post>().HasQueryFilter(p => !p.IsDeleted);
}