What is Cartesian Explosion when including multiple relationships, and how do Split Queries solve it?

Short answer

Multiple Include clauses can generate a huge JOIN query that multiplies returned rows exponentially; AsSplitQuery() splits it into separate SQL queries for each relationship.

Explanation

Suppose a blog has posts, and each post has comments and tags. .Include(p => p.Comments).Include(p => p.Tags) generates one SQL query with several LEFT JOINs. If a post has 20 comments and 10 tags, the SQL server returns 200 rows for the same post, duplicating its data (Cartesian explosion). AsSplitQuery() fetches posts, comments, and tags with separate queries and combines them safely in memory.

Code example

var blogs = await dbContext.Blogs
    .Include(b => b.Posts)
        .ThenInclude(p => p.Comments)
    .AsSplitQuery() // Prevents cartesian explosion and reduces network traffic
    .ToListAsync();

Common mistakes

• Using AsSplitQuery without considering database consistency or a transaction when data may change during the read.

Follow-up questions

• What are Compiled Queries in EF Core, and when are they worth using?

Sources

• Microsoft Learn — Single vs. Split Queries in EF Core