[ActiveRecord] 之四：Cascade

 在ActiveRecord中级联操作为我们带来很多方便，但是一些细节地方需要注意。

[ActiveRecord("Users")]public class User : ActiveRecordBase{    public User()    {    }    public User(string name) : this()    {        this.name = name;    }    private int id;    [PrimaryKey(PrimaryKeyType.Identity)]    public int Id    {        get { return id; }        set { id = value; }    }    private string name;    [Property(Unique=true)]    public string Name    {        get { return name; }        set { name = value; }    }    private Company company;    [BelongsTo("CompanyId")]    public Company Company    {        get { return company; }        set { company = value; }    }}[ActiveRecord("company")]public class Company : ActiveRecordBase{    public Company()    {    }    public Company(string name) : this()    {        this.name = name;    }    private int id;    [PrimaryKey(PrimaryKeyType.Identity)]    public int Id    {        get { return id; }        set { id = value; }    }    private string name;    [Property(NotNull=true)]    public string Name    {        get { return name; }        set { name = value; }    }    private IList users = new ArrayList();    [HasMany(typeof(User), ColumnKey = "CompanyId", Table = "Users", Cascade=ManyRelationCascadeEnum.AllDeleteOrphan)]    public IList Users    {        get { return users; }        set { users = value; }    }    public static Company Find(int id)    {        return FindByPrimaryKey(typeof(Company), id) as Company;    }}

在上面的代码中我们为 Company.Users 添加了级联操作属性。接下来我们分别验证一下在级联(Cascade=ManyRelationCascadeEnum.AllDeleteOrphan)和非级联(Cascade=ManyRelationCascadeEnum.None)方式下操作对象有什么不同。。

1. 级联方式插入：创建Company和其关联的用户，company.Create() 会自动保存company.Users中的关联对象。

using (TransactionScope trans = new TransactionScope()){    try    {        Company company = new Company("公司A");        for (int i = 1; i <= 10; i++)        {            User user = new User("用户" + i);            company.Users.Add(user);        }        company.Create();        trans.VoteCommit();    }    catch    {        trans.VoteRollBack();    }}

2. 级联方式删除：删除Company对象时，其关联的User对象也正常被删除。

Company company = Company.Find(1);company.Delete();

3. 级联方式删除：可以通过移除 Company.User 集合中的 User 对象的方式来删除 User 对象。

Company company = Company.Find(1);company.Users.RemoveAt(2);company.Update();

4. 非级联方式插入：必须先创建(保存)Company对象，而且需要指定 User.Company 属性才能正确创建所有对象。

using (TransactionScope trans = new TransactionScope()){    try    {        Company company = new Company("公司A");        company.Create();        for (int i = 1; i <= 10; i++)        {            User user = new User("用户" + i);            user.Company = company;            user.Save();        }        trans.VoteCommit();    }    catch    {        trans.VoteRollBack();    }}

5. 非级联方式删除：仅删除了Company对象自身，与之关联的User对象并未被删除，仅将其CompanyId字段设为NULL。

Company company = Company.Find(1);company.Delete(); 

6. 非级联方式删除：移除集合中子对象时，也并未真正将其删除，同样只是将其CompanyId字段设为NULL而已。

Company company = Company.Find(1);company.Users.RemoveAt(2);company.Update();

正确的做法

(company.Users[2] as User).Delete();

可见两种方式操作上有很大差异，编码时一定要注意，否则数据库中恐怕会留下许多“僵尸”数据。
在ManyToMany情况下，非级联删除时，仅会删除自身和映射表中的记录；级联删除会试图删除关联记录。