𝐖𝐡𝐚𝐭 𝐢𝐬 𝐕𝐚𝐥𝐮𝐞-𝐎𝐛𝐣𝐞𝐜𝐭 𝐚𝐧𝐝 𝐇𝐨𝐰 𝐭𝐨 𝐬𝐭𝐨𝐫𝐞 𝐢𝐭 𝐢𝐧 𝐄𝐅 𝐂𝐨𝐫𝐞?

#ddd #valueobject #efcore

⁉️ 𝐖𝐡𝐚𝐭?
A value object is an object that can be identified by the composition of its values. For instance, an address can be considered as a value object because the compositions of country/region, city, street defines it.

𝐈𝐦𝐩𝐨𝐫𝐭𝐚𝐧𝐭 𝐜𝐡𝐚𝐫𝐚𝐜𝐭𝐞𝐫𝐢𝐬𝐭𝐢𝐜𝐬 𝐨𝐟 𝐯𝐚𝐥𝐮𝐞 𝐨𝐛𝐣𝐞𝐜𝐭𝐬:
1- They do not have identity. (For example, two customers with the same name are not the same and they can be distinguished by their Ids. On the other hand, when two addresses are identical, they are the same.).

2- They are immutable. (The values of a value object must be immutable once the object is created. Therefore, when the object is created, you must provide the required values but must not allow them to change).

🌍 𝑹𝒆𝒂𝒍-𝑾𝒐𝒓𝒍𝒅 𝑺𝒄𝒆𝒏𝒂𝒓𝒊𝒐
Consider an Order aggregate root this aggregate root contains one entity named Order Item with an id since two order items with the same products are still different and a value object named address since two addresses with the same values are considered equal.

💻 𝐈𝐦𝐩𝐥𝐞𝐦𝐞𝐧𝐭 𝐕𝐚𝐥𝐮𝐞 𝐨𝐛𝐣𝐞𝐜𝐭𝐬 𝐢𝐧 𝐂#
You can have a value object base class that has basic utility methods like equality based on the comparison between all the attributes and other fundamental characteristics. Then each value object can inherit from the base class.

🗄 𝐇𝐨𝐰 𝐜𝐚𝐧 𝐰𝐞 𝐬𝐭𝐨𝐫𝐞 𝐯𝐚𝐥𝐮𝐞 𝐨𝐛𝐣𝐞𝐜𝐭𝐬 𝐢𝐧 𝐭𝐡𝐞 𝐝𝐚𝐭𝐚𝐛𝐚𝐬𝐞 𝐬𝐢𝐧𝐜𝐞 𝐭𝐡𝐞𝐲 𝐡𝐚𝐯𝐞 𝐧𝐨 𝐢𝐝𝐞𝐧𝐭𝐢𝐭𝐲?
The best way to store value objects with EF Core 2.0 and later is using owned entity type. An owned entity type allows you to map types that do not have identity. For implementing value objects, the entity should contain navigation of the value object and in configuration file owned entity should be defined.
For example, in Order entity the Address is a values object and it is implemented as an owned entity type within the owner entity.
By default, EF Core conventions name the columns for the properties of the owned entity type like EntityProperty_OwnedEntityProperty. Therefore, the properties of Address will appear in the Orders table with the names Address_Street, Address_City but you can customize with the Property().HasColumnName().