Laravel Eloquent ORM - Mismatch between generated SQL and querybuilder results when selecting all models where two relationships are both absent

Laravel’s Eloquent ORM is a powerful tool for interacting with your database, but it can sometimes behave unexpectedly. In this article, we’ll explore a common issue that arises when trying to select all models where two specific relationships are both absent.

Background and Relationships

For the sake of this explanation, let’s assume we have two models: Foobar and Baz. The relationship between these models is defined as follows:

• Foobar belongsTo Baz
• Baz hasOne Foobar

This means there is a foreign key column in the Foobar table for baz_id, which establishes the relationship.

The Issue

We want to query all Foobar instances where both the baz and quux relationships are absent. We can achieve this using Eloquent’s doesntHave method, but we encounter an unexpected result: some Foobar instances with no relationships appear in the results.

The Code

The problematic code is as follows:

$foobar->doesntHave('baz', 'AND')-
    >doesntHave('quux')-
    >get();

This query seems to be correct, but it produces unexpected results. Let’s examine what happens when we run this query in different ways.

Running the Query

We’ll run the query with different methods to understand why the results are not as expected.

First: doesntHave('baz', 'AND')->doesntHave('quux')->get();

Foobar::doesntHave('baz', 'AND')->
    >doesntHave('quux')-
    >get();
// This gets a collection that is not empty, the first item is a Foobar instance that definitely has a baz

Foobar::doesntHave('baz', 'AND')->
    >doesntHave('quux')-
    >first();
// This is null (?)

Foobar::doesntHave('baz', 'AND')->
    >doesntHave('quux')-
    >count();
// This is 0 (?)

Foobar::doesntHave('baz', 'AND')->
    >doesntHave('quux')-
    >get()->
    >get(0)->
    >baz;
// This gets the Baz object attached to the first instance

The get() method returns all matching records, while first() and count() return a single record or the number of records, respectively. However, when we use first() and then access the relationship, it’s null.

Second: Using Raw SQL

We’ll run the raw SQL query to ensure that it produces the correct results.

Foobar::doesntHave('baz', 'AND')->
    >doesntHave('quux')-
    >get()->
    >toSql();
// This outputs the generated raw SQL.

When we input this raw SQL into a SQL client, we get the expected results. However, it’s still unclear why Eloquent is producing different results.

The Solution

To fix this issue, we can use whereDoesntHave instead of doesntHave. Here’s how to rewrite our query:

Foobar::whereDoesntHave('baz')->
    >whereDoesntHave('quux')-
    >get();

Using whereDoesntHave allows us to build a SQL query with the correct conditions.

Explanation

The issue arises from how Eloquent handles relationships when building a query. When we use doesntHave, it doesn’t check for the absence of both relationships simultaneously. Instead, it checks for the presence of either relationship and then negates that using the 'AND' keyword.

However, whereDoesntHave allows us to build a SQL query with both conditions explicitly stated as separate clauses. This is why we can use whereDoesntHave('baz') followed by whereDoesntHave('quux'), ensuring that Eloquent checks for the absence of both relationships correctly.

Conclusion

Laravel’s Eloquent ORM provides an intuitive and powerful way to interact with your database, but it’s not always perfect. By understanding how Eloquent handles relationships and queries, you can write more effective code and avoid unexpected results. In this article, we explored a common issue where two relationships are both absent, but used whereDoesntHave instead of doesntHave to resolve the problem.

Additional Resources

For further reading on Laravel’s Eloquent ORM and how to use it effectively, check out the official documentation: https://laravel.com/docs/eloquent

This article covers only one specific issue with Eloquent. If you encounter other problems or want more in-depth information on using Eloquent, feel free to explore the rest of the documentation for more guidance.

Code Example

Here’s an example of how you can use whereDoesntHave:

// Retrieve all Foobar instances where baz and quux are absent
$foobars = Foobar::whereDoesntHave('baz')->
    >whereDoesntHave('quux')-
    >get();

// Output: All Foobar instances with no relationships

By following this example, you can use whereDoesntHave to build SQL queries that correctly check for the absence of multiple relationships.

Last modified on 2024-01-10