c# - Entity Framework 父 -> 子链接和外键约束失败错误

Question

我正在使用 Entity Framework 7(核心)和 Sqlite 数据库。当前使用 comboBox 通过此方法更改实体类别:

/// <summary>
/// Changes the given device gategory.
/// </summary>
/// <param name="device"></param>
/// <param name="category"></param>
public bool ChangeCategory(Device device, Category category)
{
    if (device != null && category != null )
    {
        try
        {
            var selectedCategory = FxContext.Categories.SingleOrDefault(s => s.Name == category.Name);
            if (selectedCategory == null) return false;
            if (device.Category1 == selectedCategory) return true;

            device.Category1 = selectedCategory;
            device.Category = selectedCategory.Name;
            device.TimeCreated = DateTime.Now;
            return true;
        }
        catch (Exception ex)
        {
            throw new InvalidOperationException("Category change for device failed. Possible reason: database has multiple categories with same name.");
        }
    }
    return false;
}

此函数可以很好地更改 device 的类别 ID。但这是正确的方法吗？

链接后，稍后在删除此 category 时，我从 Sqlite 数据库中收到错误消息:

{"SQLite Error 19: 'FOREIGN KEY constraint failed'"}

删除类别的方法

public bool RemoveCategory(Category category)
{
    if (category == null) return false;
    var itemForDeletion = FxContext.Categories
        .Where(d => d.CategoryId == category.CategoryId);
    FxContext.Categories.RemoveRange(itemForDeletion);
    return true;
}

编辑以下是 device 和 category 的结构:

CREATE TABLE "Category" (
    "CategoryId" INTEGER NOT NULL CONSTRAINT "PK_Category" PRIMARY KEY AUTOINCREMENT,
    "Description" TEXT,
    "HasErrors" INTEGER NOT NULL,
    "IsValid" INTEGER NOT NULL,
    "Name" TEXT
)

CREATE TABLE "Device" (
    "DeviceId" INTEGER NOT NULL CONSTRAINT "PK_Device" PRIMARY KEY AUTOINCREMENT,
    "Category" TEXT,
    "Category1CategoryId" INTEGER,
    CONSTRAINT "FK_Device_Category_Category1CategoryId" FOREIGN KEY ("Category1CategoryId") REFERENCES "Category" ("CategoryId") ON DELETE RESTRICT,
)

Answer 1

您的 SQLite 表有外键限制 ON DELETE RESTRICT。这意味着如果 Devices 中的任何行仍然指向您要删除的类别，SQLite 数据库将阻止此操作。要解决此问题，您可以 (1) 明确地将所有设备更改为不同的类别，或者 (2) 将 ON DELETE 行为更改为其他内容，例如 CASCADE 或 SET NULL。参见 https://www.sqlite.org/foreignkeys.html#fk_actions

如果您已使用 EF 创建表，请将您的模型配置为使用不同的删除行为。默认是限制。参见 https://docs.efproject.net/en/latest/modeling/relationships.html#id2 .示例:

        modelBuilder.Entity<Post>()
            .HasOne(p => p.Blog)
            .WithMany(b => b.Posts)
            .OnDelete(DeleteBehavior.Cascade);