英文:
How to add a comment to owned JSON column in EF Core?
问题
"HasComment"调用在尝试使用dotnet ef migrations add创建迁移时会导致失败。给出的消息是：
System.InvalidOperationException: 因为它被配置为导航，所以无法将'Metadata'用作实体类型'MyEntity'的属性。
我理解这个问题的原因可能是因为如果明天我选择将这个'Metadata'存储在单独的表中，那么就无法再有“列注释”了。如何覆盖此行为并添加注释呢？
我唯一想到的方法是手动编辑迁移以添加注释，但这意味着如果我们将来想要编辑注释，就必须再次手动编辑它，所以我更喜欢让EF Core为我们生成指令。
英文:
Given an EF Core entity with an owned type that's stored in a JSON column like so
public class MyEntity
{
public MyEntity( SomeMetadata metadata) : this()
{
Metadata = metadata;
}
/// <summary>
/// Just for EntityFramework because it can't handle a constructor with owned type.
/// </summary>
private MyEntity()
{
}
public Guid PrimaryId { get; private set; }
public SomeMetadata Metadata { get; private set; }
public class SomeMetadata
{
public string? SomeNestedThing { get; set; }
}
}
public class MyEntityConfiguration : IEntityTypeConfiguration<MyEntity>
{
public void Configure(EntityTypeBuilder<MyEntity> builder)
{
builder.OwnsOne(e => e.Metadata, ownedNavigationBuilder =>
{
ownedNavigationBuilder.ToJson();
});
builder.Property(e => e.Metadata)
.HasComment("Comment about this JSON column");
}
}
The HasComment call will result in a failure when trying to create a migration using dotnet ef migrations add. The message given is
> System.InvalidOperationException: 'Metadata' cannot be used as a property on entity type 'MyEntity' because it is configured as a navigation.
I understand that the reason for this is probably because if tomorrow I choose to store this Metadata in a separate table, then I can't have a "column comment" anymore. How can I go about overriding this and adding a comment?
The only thing I've come up with is editing the migration manually to add a comment, but this means that if we want to edit a comment later in the future, we'd have to manually edit it again, so I'd prefer to let EF Core generate the instruction for us.
答案1
得分: 1
Metadata 不是表中的列，它是一个导航属性，应该指向另一张表中包含所需信息的记录。
然而，在您的情况下，您实际上不需要一个导航属性。您可以简单地调整您的代码，使 "JSON" 列成为一个字符串。
public MyEntity(SomeMetadata metadata) : this()
{
Metadata = metadata.SomeNestedThing;
}
public string Metadata { get; private set; }
在进行这些更改之后，Metadata 将成为表中的一个实际列，您用于添加评论的代码将会起作用。
英文:
Metadata is not a column in a table, it is a navigation property, which should point to a record in another table that holds your desired info.
However, in your scenario, you don't really need a navigation property. You can just adjust your code so that the "JSON" column is a string.
public MyEntity(SomeMetadata metadata) : this()
{
Metadata = metadata.SomeNestedThing;
}
public string Metadata { get; private set; }
After these changes, Metadata will be an actual column in the table and your code for adding the comment will work.
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