EF Core 5.0 — Many to Many Relationship

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This post originally posted in my blog. You can find it here.

There is a new feature in EF 5.0 that change the way to create the Many-to-Many Relationship. It is really convenient way to create a relationship with Entities. Before dive into that let’s check that, how we create a many-to-many relationship in previous versions.

Before EF Core 5.0

Let’s take our common scenario with Post and Tag example. A blog post can have multiple tags and one tag can be tagged with many posts.

This is our Post entity.

This is out Tag entity.

So these 2 entities have a many-to-many relationship. Let’s create the joining entity that contains all the mapping details with both entities.

This PostId and TagId works as composite primary key

Now we need to add this mapping to our Post and Tag entities.

Now we are at the last step. We use the Fluent API to define the primary keys of the PostTag .

That’s it. Once we enable the migration this will create a table called PostTag and it has a composite primary key and has a relation with Post and Tag tables.

If you defined the keys in PostTag class differently you need to mention it in OnModelCreating by using Fluent API.

Hola, that is lots of code. Now let’s see how what are an improvement with EF Core 5.0

EF Core 5.0

Create the Post entity with navigation property.

Create the Tag entity with navigation property.

That’s it. Now EF Core will identify this as a many-to-many relationship and it will create a table PostTag . The PostTag table data can be query and update without explicitly referring to that table. If we need more modification we can use Fluent API as well.

I will wrap up this post from here. If you have anything to ask regarding this please leave a comment here. Also, I wrote this according to my understanding. So if any point is wrong, don’t hesitate to correct me. I really appreciate you.

That’s for today friends. See you soon. Thank you.

References:

What’s New in EF Core 5.0