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ジャンルのカテゴリ―名

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内容の要旨

<p data-bm="16" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: 4px; padding: revert; -webkit-line-clamp: revert; color: rgba(0, 0, 0, 0.8); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;" data-pasted="true">はい、<br><code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255);">public ICollection&lt;IncomeType&gt; IncomeTypes { get; set; } = new List&lt;IncomeType&gt;();</code><br>のようなコードは、<strong style="font-weight: 700;">ASP.NET Core MVC + Entity Framework Core</strong> で&nbsp;<strong style="font-weight: 700;">1対多 (One-to-Many) または多対多 (Many-to-Many)</strong> のリレーションをモデルに定義する場合に必要です。</p><h2 data-bm="17" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; font: 22px / 24px Roboto, Helvetica, sans-serif; height: 32px; -webkit-line-clamp: 1; overflow: hidden; text-overflow: ellipsis; display: -webkit-box; -webkit-box-orient: vertical; color: rgba(0, 0, 0, 0.8); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">1. このコードが必要なケース</h2><ul data-bm="18" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; color: rgba(0, 0, 0, 0.8); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;"><strong style="font-weight: 700;">親エンティティが複数の子エンティティを持つ場合</strong><ul style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert;"><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;">例:&nbsp;<code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255);">IncomeCategory</code> が複数の&nbsp;<code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255);">IncomeType</code> を持つ</li></ul></li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;"><strong style="font-weight: 700;">ナビゲーションプロパティを使って関連データを取得・保存したい場合</strong></li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;"><strong style="font-weight: 700;">EF Core の遅延読み込み / 明示的読み込み / 即時読み込みで関連データを扱う場合</strong></li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;"><strong style="font-weight: 700;">新規作成時にコレクションを初期化して NullReferenceException を防ぎたい場合</strong></li></ul><h2 data-bm="19" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; font: 22px / 24px Roboto, Helvetica, sans-serif; height: 32px; -webkit-line-clamp: 1; overflow: hidden; text-overflow: ellipsis; display: -webkit-box; -webkit-box-orient: vertical; color: rgba(0, 0, 0, 0.8); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">2. 完全なモデルとリレーション設定例</h2><h3 data-bm="20" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; display: inline-block; font: 400 20px / 22px Roboto, Helvetica, sans-serif; color: rgba(0, 0, 0, 0.8); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">モデル定義</h3><pre data-priority="2" data-bm="21" style="background: none 0% 0% / auto repeat scroll padding-box border-box rgb(245, 245, 245); border: 1px solid rgba(0, 0, 0, 0.1); border-radius: 8px; overflow: hidden; color: rgba(0, 0, 0, 0.8); font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><div data-bm="31" style="display: flex; height: 28px; flex-direction: row; justify-content: space-between; align-items: center; gap: 8px; padding: 8px 12px; border-bottom: 1px solid rgba(0, 0, 0, 0.1); background: none 0% 0% / auto repeat scroll padding-box border-box rgb(248, 244, 241);"><h5 style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: 0px; padding: revert; font-style: normal !important; font-variant: normal !important; font-weight: 400 !important; font-stretch: 100% !important; line-height: 18px; font-family: Roboto, Helvetica, sans-serif !important; font-optical-sizing: auto !important; font-size-adjust: none !important; font-kerning: auto !important; font-feature-settings: normal !important; font-variation-settings: normal !important; font-language-override: normal !important; font-size: 16px; display: inline-block; color: rgb(60, 81, 180);">Csharp</h5><div style="height: 28px;"><button type="button" tabindex="" title="Copy code" style="box-sizing: border-box; margin: 0px; padding: 0px; font: 400 13px / 20px Roboto, Helvetica, sans-serif; background-color: rgb(217, 223, 251); border: 1px solid rgba(0, 0, 0, 0); display: grid; grid-auto-flow: column; align-items: center; cursor: pointer; color: rgb(60, 81, 180) !important; text-decoration: none !important; border-radius: 9999px; block-size: 28px; gap: 2px; padding-inline: 10px;"><div style="box-sizing: border-box; margin: 0px; padding: 0px; min-inline-size: 0px; max-inline-size: 100%; white-space: nowrap; text-overflow: ellipsis; overflow: clip; max-block-size: calc(1lh); padding-inline: 2px;">Copy code</div></button></div></div><code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255); display: block; white-space: pre-wrap; overflow-wrap: anywhere; padding: 8px 16px 16px;"><span style="color: rgb(215, 58, 73);">using</span> System.Collections.Generic;
<span style="color: rgb(215, 58, 73);">using</span> System.ComponentModel.DataAnnotations;

<span style="color: rgb(215, 58, 73);">namespace</span> <span style="color: rgb(111, 66, 193);">MyApp.Models</span>
{
    <span style="color: rgb(106, 115, 125);">// 親モデル: 収入カテゴリ</span>
    <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(215, 58, 73);">class</span> <span style="color: rgb(111, 66, 193);">IncomeCategory</span>
    {
        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(227, 98, 9);">int</span> Id { <span style="color: rgb(215, 58, 73);">get</span>; <span style="color: rgb(215, 58, 73);">set</span>; }

        [<span style="color: rgb(0, 92, 197);">Required</span>]
        [<span style="color: rgb(0, 92, 197);">StringLength(100)</span>]
        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(227, 98, 9);">string</span> Name { <span style="color: rgb(215, 58, 73);">get</span>; <span style="color: rgb(215, 58, 73);">set</span>; }

        <span style="color: rgb(106, 115, 125);">// 1対多: IncomeCategory &rarr; IncomeType</span>
        <span style="color: rgb(215, 58, 73);">public</span> ICollection&lt;IncomeType&gt; IncomeTypes { <span style="color: rgb(215, 58, 73);">get</span>; <span style="color: rgb(215, 58, 73);">set</span>; } = <span style="color: rgb(215, 58, 73);">new</span> List&lt;IncomeType&gt;();
    }

    <span style="color: rgb(106, 115, 125);">// 子モデル: 収入タイプ</span>
    <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(215, 58, 73);">class</span> <span style="color: rgb(111, 66, 193);">IncomeType</span>
    {
        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(227, 98, 9);">int</span> Id { <span style="color: rgb(215, 58, 73);">get</span>; <span style="color: rgb(215, 58, 73);">set</span>; }

        [<span style="color: rgb(0, 92, 197);">Required</span>]
        [<span style="color: rgb(0, 92, 197);">StringLength(100)</span>]
        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(227, 98, 9);">string</span> TypeName { <span style="color: rgb(215, 58, 73);">get</span>; <span style="color: rgb(215, 58, 73);">set</span>; }

        <span style="color: rgb(106, 115, 125);">// 外部キー</span>
        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(227, 98, 9);">int</span> IncomeCategoryId { <span style="color: rgb(215, 58, 73);">get</span>; <span style="color: rgb(215, 58, 73);">set</span>; }

        <span style="color: rgb(106, 115, 125);">// ナビゲーションプロパティ</span>
        <span style="color: rgb(215, 58, 73);">public</span> IncomeCategory IncomeCategory { <span style="color: rgb(215, 58, 73);">get</span>; <span style="color: rgb(215, 58, 73);">set</span>; }
    }
}
</code></pre><h3 data-bm="22" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; display: inline-block; font: 400 20px / 22px Roboto, Helvetica, sans-serif; color: rgba(0, 0, 0, 0.8); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">DbContext 設定</h3><pre data-priority="2" data-bm="23" style="background: none 0% 0% / auto repeat scroll padding-box border-box rgb(245, 245, 245); border: 1px solid rgba(0, 0, 0, 0.1); border-radius: 8px; overflow: hidden; color: rgba(0, 0, 0, 0.8); font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><div data-bm="32" style="display: flex; height: 28px; flex-direction: row; justify-content: space-between; align-items: center; gap: 8px; padding: 8px 12px; border-bottom: 1px solid rgba(0, 0, 0, 0.1); background: none 0% 0% / auto repeat scroll padding-box border-box rgb(248, 244, 241);"><h5 style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: 0px; padding: revert; font-style: normal !important; font-variant: normal !important; font-weight: 400 !important; font-stretch: 100% !important; line-height: 18px; font-family: Roboto, Helvetica, sans-serif !important; font-optical-sizing: auto !important; font-size-adjust: none !important; font-kerning: auto !important; font-feature-settings: normal !important; font-variation-settings: normal !important; font-language-override: normal !important; font-size: 16px; display: inline-block; color: rgb(60, 81, 180);">Csharp</h5><div style="height: 28px;"><button type="button" tabindex="" title="Copy code" style="box-sizing: border-box; margin: 0px; padding: 0px; font: 400 13px / 20px Roboto, Helvetica, sans-serif; background-color: rgb(217, 223, 251); border: 1px solid rgba(0, 0, 0, 0); display: grid; grid-auto-flow: column; align-items: center; cursor: pointer; color: rgb(60, 81, 180) !important; text-decoration: none !important; border-radius: 9999px; block-size: 28px; gap: 2px; padding-inline: 10px;"><div style="box-sizing: border-box; margin: 0px; padding: 0px; min-inline-size: 0px; max-inline-size: 100%; white-space: nowrap; text-overflow: ellipsis; overflow: clip; max-block-size: calc(1lh); padding-inline: 2px;">Copy code</div></button></div></div><code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255); display: block; white-space: pre-wrap; overflow-wrap: anywhere; padding: 8px 16px 16px;"><span style="color: rgb(215, 58, 73);">using</span> Microsoft.EntityFrameworkCore;
<span style="color: rgb(215, 58, 73);">using</span> MyApp.Models;

<span style="color: rgb(215, 58, 73);">namespace</span> <span style="color: rgb(111, 66, 193);">MyApp.Data</span>
{
    <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(215, 58, 73);">class</span> <span style="color: rgb(111, 66, 193);">ApplicationDbContext</span> : <span style="color: rgb(111, 66, 193);">DbContext</span>
    {
        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(111, 66, 193);">ApplicationDbContext</span>(DbContextOptions&lt;ApplicationDbContext&gt; options)
            : <span style="color: rgb(111, 66, 193);">base</span>(options) { }

        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(111, 66, 193);">DbSet</span>&lt;<span style="color: rgb(111, 66, 193);">IncomeCategory</span>&gt; IncomeCategories { <span style="color: rgb(215, 58, 73);">get</span>; <span style="color: rgb(215, 58, 73);">set</span>; }
        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(111, 66, 193);">DbSet</span>&lt;<span style="color: rgb(111, 66, 193);">IncomeType</span>&gt; IncomeTypes { <span style="color: rgb(215, 58, 73);">get</span>; <span style="color: rgb(215, 58, 73);">set</span>; }

        <span style="color: rgb(215, 58, 73);">protected</span> <span style="color: rgb(215, 58, 73);">override</span> <span style="color: rgb(215, 58, 73);">void</span> <span style="color: rgb(111, 66, 193);">OnModelCreating</span>(ModelBuilder modelBuilder)
        {
            <span style="color: rgb(215, 58, 73);">base</span>.OnModelCreating(modelBuilder);

            <span style="color: rgb(106, 115, 125);">// 1対多のリレーション設定</span>
            modelBuilder.Entity&lt;IncomeCategory&gt;()
                .HasMany(c =&gt; c.IncomeTypes)
                .WithOne(t =&gt; t.IncomeCategory)
                .HasForeignKey(t =&gt; t.IncomeCategoryId)
                .OnDelete(DeleteBehavior.Cascade);
        }
    }
}
</code></pre><h3 data-bm="24" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; display: inline-block; font: 400 20px / 22px Roboto, Helvetica, sans-serif; color: rgba(0, 0, 0, 0.8); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">マイグレーションとDB作成</h3><pre data-priority="2" data-bm="25" style="background: none 0% 0% / auto repeat scroll padding-box border-box rgb(245, 245, 245); border: 1px solid rgba(0, 0, 0, 0.1); border-radius: 8px; overflow: hidden; color: rgba(0, 0, 0, 0.8); font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><div data-bm="33" style="display: flex; height: 28px; flex-direction: row; justify-content: space-between; align-items: center; gap: 8px; padding: 8px 12px; border-bottom: 1px solid rgba(0, 0, 0, 0.1); background: none 0% 0% / auto repeat scroll padding-box border-box rgb(248, 244, 241);"><h5 style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: 0px; padding: revert; font-style: normal !important; font-variant: normal !important; font-weight: 400 !important; font-stretch: 100% !important; line-height: 18px; font-family: Roboto, Helvetica, sans-serif !important; font-optical-sizing: auto !important; font-size-adjust: none !important; font-kerning: auto !important; font-feature-settings: normal !important; font-variation-settings: normal !important; font-language-override: normal !important; font-size: 16px; display: inline-block; color: rgb(60, 81, 180);">Bash</h5><div style="height: 28px;"><button type="button" tabindex="" title="Copy code" style="box-sizing: border-box; margin: 0px; padding: 0px; font: 400 13px / 20px Roboto, Helvetica, sans-serif; background-color: rgb(217, 223, 251); border: 1px solid rgba(0, 0, 0, 0); display: grid; grid-auto-flow: column; align-items: center; cursor: pointer; color: rgb(60, 81, 180) !important; text-decoration: none !important; border-radius: 9999px; block-size: 28px; gap: 2px; padding-inline: 10px;"><div style="box-sizing: border-box; margin: 0px; padding: 0px; min-inline-size: 0px; max-inline-size: 100%; white-space: nowrap; text-overflow: ellipsis; overflow: clip; max-block-size: calc(1lh); padding-inline: 2px;">Copy code</div></button></div></div><code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255); display: block; white-space: pre-wrap; overflow-wrap: anywhere; padding: 8px 16px 16px;">dotnet ef migrations add InitialCreate
dotnet ef database update
</code></pre><h3 data-bm="26" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; display: inline-block; font: 400 20px / 22px Roboto, Helvetica, sans-serif; color: rgba(0, 0, 0, 0.8); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">コントローラー例（関連データの取得）</h3><pre data-priority="2" data-bm="27" style="background: none 0% 0% / auto repeat scroll padding-box border-box rgb(245, 245, 245); border: 1px solid rgba(0, 0, 0, 0.1); border-radius: 8px; overflow: hidden; color: rgba(0, 0, 0, 0.8); font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><div data-bm="34" style="display: flex; height: 28px; flex-direction: row; justify-content: space-between; align-items: center; gap: 8px; padding: 8px 12px; border-bottom: 1px solid rgba(0, 0, 0, 0.1); background: none 0% 0% / auto repeat scroll padding-box border-box rgb(248, 244, 241);"><h5 style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: 0px; padding: revert; font-style: normal !important; font-variant: normal !important; font-weight: 400 !important; font-stretch: 100% !important; line-height: 18px; font-family: Roboto, Helvetica, sans-serif !important; font-optical-sizing: auto !important; font-size-adjust: none !important; font-kerning: auto !important; font-feature-settings: normal !important; font-variation-settings: normal !important; font-language-override: normal !important; font-size: 16px; display: inline-block; color: rgb(60, 81, 180);">Csharp</h5><div style="height: 28px;"><button type="button" tabindex="" title="Copy code" style="box-sizing: border-box; margin: 0px; padding: 0px; font: 400 13px / 20px Roboto, Helvetica, sans-serif; background-color: rgb(217, 223, 251); border: 1px solid rgba(0, 0, 0, 0); display: grid; grid-auto-flow: column; align-items: center; cursor: pointer; color: rgb(60, 81, 180) !important; text-decoration: none !important; border-radius: 9999px; block-size: 28px; gap: 2px; padding-inline: 10px;"><div style="box-sizing: border-box; margin: 0px; padding: 0px; min-inline-size: 0px; max-inline-size: 100%; white-space: nowrap; text-overflow: ellipsis; overflow: clip; max-block-size: calc(1lh); padding-inline: 2px;">Copy code</div></button></div></div><code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255); display: block; white-space: pre-wrap; overflow-wrap: anywhere; padding: 8px 16px 16px;"><span style="color: rgb(215, 58, 73);">using</span> Microsoft.AspNetCore.Mvc;
<span style="color: rgb(215, 58, 73);">using</span> Microsoft.EntityFrameworkCore;
<span style="color: rgb(215, 58, 73);">using</span> MyApp.Data;

<span style="color: rgb(215, 58, 73);">namespace</span> <span style="color: rgb(111, 66, 193);">MyApp.Controllers</span>
{
    <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(215, 58, 73);">class</span> <span style="color: rgb(111, 66, 193);">IncomeCategoriesController</span> : <span style="color: rgb(111, 66, 193);">Controller</span>
    {
        <span style="color: rgb(215, 58, 73);">private</span> <span style="color: rgb(215, 58, 73);">readonly</span> ApplicationDbContext _context;

        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(111, 66, 193);">IncomeCategoriesController</span>(ApplicationDbContext context)
        {
            _context = context;
        }

        <span style="color: rgb(215, 58, 73);">public</span> <span style="color: rgb(215, 58, 73);">async</span> Task&lt;IActionResult&gt; <span style="color: rgb(111, 66, 193);">Index</span>()
        {
            <span style="color: rgb(106, 115, 125);">// Includeで関連データを同時取得</span>
            <span style="color: rgb(215, 58, 73);">var</span> categories = <span style="color: rgb(215, 58, 73);">await</span> _context.IncomeCategories
                .Include(c =&gt; c.IncomeTypes)
                .ToListAsync();

            <span style="color: rgb(215, 58, 73);">return</span> View(categories);
        }
    }
}
</code></pre><h3 data-bm="28" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; display: inline-block; font: 400 20px / 22px Roboto, Helvetica, sans-serif; color: rgba(0, 0, 0, 0.8); letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">ポイント</h3><ul data-bm="29" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: revert; padding: revert; color: rgba(0, 0, 0, 0.8); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;"><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;"><strong style="font-weight: 700;"><code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255);">ICollection&lt;IncomeType&gt;</code></strong> は、EF Core がリレーションを認識し、関連データを格納するためのナビゲーションプロパティ。</li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;"><strong style="font-weight: 700;"><code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255);">= new List&lt;IncomeType&gt;()</code></strong> により、インスタンス生成時にコレクションが初期化され、<code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255);">NullReferenceException</code> を防ぐ。</li><li style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin-top: revert; margin-right: revert; margin-bottom: 8px; margin-left: revert; padding: revert;"><strong style="font-weight: 700;"><code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255);">HasMany</code> /&nbsp;<code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255);">WithOne</code></strong> で明示的にリレーションを設定すると、外部キーや削除動作を制御できる。</li></ul><p data-bm="30" style="border: 0px; border-collapse: collapse; border-spacing: 0px; list-style-position: initial; list-style-image: initial; list-style-type: revert; margin: 4px; padding: revert; -webkit-line-clamp: revert; color: rgba(0, 0, 0, 0.8); font-family: Roboto, Helvetica, sans-serif; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; white-space: normal; background-color: rgb(255, 255, 255); text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">もし希望があれば、このモデルを使った&nbsp;<strong style="font-weight: 700;">Create/Edit ビューで IncomeType を同時に登録するフォーム例</strong> も作れますが、<br>それも含めて作りますか？<br>そうすれば、<code style="border-radius: 8px; background: none 0% 0% / auto repeat scroll padding-box border-box rgb(255, 255, 255);">IncomeTypes</code> を持つケースがより実践的に理解できます。</p><p data-f-id="pbf" style="text-align: center; font-size: 14px; margin-top: 30px; opacity: 0.65; font-family: sans-serif;">Powered by <a href="https://www.froala.com/wysiwyg-editor?pb=1" title="Froala Editor">Froala Editor</a></p>

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