𝗨𝗻𝗱𝗲𝗿𝘀𝘁𝗮𝗻𝗱𝗶𝗻𝗴 𝗩𝗮𝗹𝘂𝗲 𝗢𝗯𝗷𝗲𝗰𝘁𝘀 𝗮𝗻𝗱 𝘁𝗵𝗲 𝗢𝘄𝗻𝘀𝗢𝗻𝗲() 𝗠𝗲𝘁𝗵𝗼𝗱 𝗶𝗻 𝗘𝗙 𝗖𝗼𝗿𝗲

As part of building my 𝗘𝗺𝗽𝗹𝗼𝘆𝗲𝗲 𝗣𝗲𝗿𝗳𝗼𝗿𝗺𝗮𝗻𝗰𝗲 𝗥𝗲𝘃𝗶𝗲𝘄 project, I learned about 𝗩𝗮𝗹𝘂𝗲 𝗢𝗯𝗷𝗲𝗰𝘁𝘀 in Domain-Driven Design and how EF Core uses the OwnsOne() method to handle them in the database context.

𝗪𝗵𝗮𝘁 𝗮𝗿𝗲 𝗩𝗮𝗹𝘂𝗲 𝗢𝗯𝗷𝗲𝗰𝘁𝘀?
Value Objects represent a concept with 𝗻𝗼 𝗶𝗱𝗲𝗻𝘁𝗶𝘁𝘆 but 𝗺𝗲𝗮𝗻𝗶𝗻𝗴𝗳𝘂𝗹 𝗲𝗾𝘂𝗮𝗹𝗶𝘁𝘆 based on their data. They are often used to model things like Score, Money, or Email in a domain.

𝗘𝘅𝗮𝗺𝗽𝗹𝗲:

public sealed class ReviewScore
{
public int Value { get; }
private ReviewScore(int value) => Value = value;
}

𝗪𝗵𝘆 𝘂𝘀𝗲 𝗢𝘄𝗻𝘀𝗢𝗻𝗲()?
In EF Core, OwnsOne() tells the framework that a property (like a value object) is 𝗼𝘄𝗻𝗲𝗱 𝗯𝘆 𝘁𝗵𝗲 𝗽𝗮𝗿𝗲𝗻𝘁 𝗲𝗻𝘁𝗶𝘁𝘆 and doesn't have its own identity table. This simplifies the data model and keeps domain integrity.

𝗗𝗼 𝘄𝗲 𝘂𝘀𝗲 𝗢𝘄𝗻𝘀𝗢𝗻𝗲() 𝗼𝗻𝗹𝘆 𝗳𝗼𝗿 𝗩𝗮𝗹𝘂𝗲 𝗢𝗯𝗷𝗲𝗰𝘁𝘀?
Typically yes, OwnsOne() is meant for 𝘃𝗮𝗹𝘂𝗲 𝗼𝗯𝗷𝗲𝗰𝘁𝘀 and 𝗰𝗼𝗺𝗽𝗹𝗲𝘅 𝘁𝘆𝗽𝗲𝘀 that are fully dependent on the parent entity.

𝗛𝗼𝘄 𝗵𝗮𝘃𝗲 𝘆𝗼𝘂 𝘂𝘀𝗲𝗱 𝗢𝘄𝗻𝘀𝗢𝗻𝗲() 𝗼𝗿 𝗩𝗮𝗹𝘂𝗲 𝗢𝗯𝗷𝗲𝗰𝘁𝘀 𝗶𝗻 𝘆𝗼𝘂𝗿 𝗽𝗿𝗼𝗷𝗲𝗰𝘁𝘀, 𝗮𝗻𝗱 𝘄𝗵𝗮𝘁 𝗽𝗮𝘁𝘁𝗲𝗿𝗻𝘀 𝗵𝗮𝘃𝗲 𝘄𝗼𝗿𝗸𝗲𝗱 𝘄𝗲𝗹𝗹 𝗳𝗼𝗿 𝘆𝗼𝘂?