Castle ActiveRecord 實戰（4）：一對多關聯映射全解析——HasMany 與 BelongsTo 雙向關聯與級聯策略

資料庫結構：外鍵關聯

CREATE TABLE Blogs (
    blog_id int IDENTITY PRIMARY KEY,
    blog_name varchar(50),
    blog_author varchar(50)
);

CREATE TABLE Posts (
    post_id int IDENTITY PRIMARY KEY,
    post_title varchar(50),
    post_contents text,
    post_categories varchar(50),
    post_blogid int FOREIGN KEY REFERENCES Blogs(blog_id),
    post_created datetime,
    post_published bit
);

雙向映射：一端 HasMany，一端 BelongsTo

Blog 端（一的一方）

[ActiveRecord("Blogs")]
public class Blog : ActiveRecordBase {
    [PrimaryKey(PrimaryKeyType.Native, "blog_id")]
    public int Id { get; set; }

    [Property("blog_name")] public string Name { get; set; }
    [Property("blog_author")] public string Author { get; set; }

    [HasMany(typeof(Post), Table = "posts", ColumnKey = "post_blogid")]
    public IList Posts { get; set; }
}

Post 端（多的一方）

[ActiveRecord("Posts")]
public class Post : ActiveRecordBase {
    [PrimaryKey(PrimaryKeyType.Native, "post_id")]
    public int Id { get; set; }

    [Property("post_title")] public string Title { get; set; }
    [Property(Column = "post_contents", ColumnType = "StringClob")] public string Contents { get; set; }
    [Property("post_categories")] public string Category { get; set; }
    [Property("post_created")] public DateTime Created { get; set; }
    [Property("post_published")] public bool Published { get; set; }

    [BelongsTo("post_blogid")]
    public Blog Blog { get; set; }
}

HasMany 關鍵屬性詳解

BelongsTo 關鍵屬性詳解

級聯操作實戰：從 SaveUpdate 到 AllDeleteOrphan

場景 1：新增 Blog 同時新增 Posts

[Test]
public void TestCascadingSave() {
    var blog = new Blog { Name = "Terrylee's Tech Space", Author = "Terrylee" };
    using (var tran = new TransactionScope()) {
        try {
            blog.Create();
            for (int i = 1; i <= 10; i++) {
                var post = new Post {
                    Title = $"This is my {i} post",
                    Category = "Castle",
                    Blog = blog // 設定關聯
                };
                post.Save();
            }
            tran.VoteCommit();
        } catch { tran.VoteRollBack(); }
    }
}

場景 2：更新 Blog 時級聯儲存新增的 Posts

需在 HasMany 設 Cascade = ManyRelationCascadeEnum.SaveUpdate：

[HasMany(typeof(Post), Table = "posts", ColumnKey = "post_blogid", 
    Cascade = ManyRelationCascadeEnum.SaveUpdate)]
public IList Posts { get; set; }

[Test]
public void TestCascadingUpdate() {
    var blog = Blog.Find(5);
    using (var tran = new TransactionScope()) {
        try {
            for (int i = 1; i <= 5; i++) {
                var post = new Post {
                    Title = $"New post {i}",
                    Category = "Castle",
                    Blog = blog
                };
                blog.Posts.Add(post); // 加入集合
                // post.Save() 可省略，SaveUpdate 級聯會自動持久化
            }
            blog.Update();
            tran.VoteCommit();
        } catch { tran.VoteRollBack(); }
    }
}

場景 3：移除集合項目時自動刪除孤兒記錄

設 Cascade = ManyRelationCascadeEnum.AllDeleteOrphan：

[Test]
public void TestCascadingUpdateDel() {
    var blog = Blog.Find(7);
    var before = blog.Posts.Count;
    using (var tran = new TransactionScope()) {
        try {
            blog.Posts.RemoveAt(0); // 移除第一篇
            blog.Update(); // 自動刪除對應 Post 記錄
            tran.VoteCommit();
        } catch { tran.VoteRollBack(); }
    }
    Assert.AreEqual(before - 1, Blog.Find(7).Posts.Count);
}

場景 4：刪除 Blog 級聯刪除所有 Posts

設 Cascade = ManyRelationCascadeEnum.All 或 AllDeleteOrphan：

[Test]
public void TestCascadingDelete() {
    var blog = Blog.Find(5);
    using (var tran = new TransactionScope()) {
        try {
            blog.Delete(); // 連帶刪除所有 Posts
            tran.VoteCommit();
        } catch { tran.VoteRollBack(); }
    }
}

Inverse = true：避免雙向更新外鍵衝突

在 HasMany 加上 Inverse = true，表示外鍵由 BelongsTo 端（Post.Blog）維護：

[HasMany(typeof(Post), Table = "posts", ColumnKey = "post_blogid", 
    Inverse = true, Cascade = ManyRelationCascadeEnum.AllDeleteOrphan)]
public IList Posts { get; set; }

這樣 Blog.Save/Update 時不會嘗試更新 post_blogid，由 Post 端統一管理，避免重複 UPDATE 與死結。

多對一：與一對多映射相同，僅視角不同

若從 Post 角度看，屬於一個 Blog，即為 BelongsTo；從 Blog 角度看，擁有多個 Posts，即為 HasMany。映射設定完全一致，無需額外學習。

總結

一對多映射核心在於 HasMany（集合端）與 BelongsTo（參考端）雙向配合。關鍵在於：正確設定 ColumnKey/Column 對應外鍵、配置 Inverse=true 避免雙向維護衝突、根據業務需求選擇 Cascade 模式（推薦 AllDeleteOrphan 實現完整生命週期管理）。掌握這些，即可靈活處理主從關聯業務。