Efcore

In this tutorial, we will understand what cartesian explosion is and how to solve that problem. Let’s look at this query:

var people = await ctx.People
   .Include(p => p.Emails)
   .Include(p => p.Addresses)
   .ToListAsync();

It translates to:

 SELECT "p"."Id", "p"."FirstName", "p"."LastName", "e"."Id", "e"."PersonEmail", "e"."PersonId", "a"."Id", "a"."PersonAddress", "a"."PersonId"
      FROM "People" AS "p"
      LEFT JOIN "Emails" AS "e" ON "p"."Id" = "e"."PersonId"
      LEFT JOIN "Addresses" AS "a" ON "p"."Id" = "a"."PersonId"
      ORDER BY "p"."Id", "e"."Id"

• Person joins with Email and Address. Both joins are at the same level.
• A person can have multiple emails and adressess.

Let’s say a person with id = 1 have 10 emails and 10 addresses. The query returns 1x10x10 = 100 rows for 1 person. It is just for one person, how much they can be for 100 people. This problem is known as cartesian explosion