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Learn how to filter users based on a custom `balance` column derived from a related table using Eloquent in Laravel.
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Filtering Users by Balance in Laravel Eloquent Queries

In Laravel, Eloquent makes it easy to work with relationships and retrieve data, but sometimes things can get tricky, especially when you're trying to filter results based on computed columns from related tables. One common scenario is wanting to filter users based on a custom balance column that’s derived from a related transactions table. In this post, we’ll tackle a query to sum the values of the credit_movement column and subsequently filter users whose balance is negative.

Understanding the Problem

You might start by wanting to get users along with their transactions' total balance. This is typically done with the withCount method to compute the balance like this:

[[See Video to Reveal this Text or Code Snippet]]

This query returns users along with their balance. However, the challenge arises when you want to filter those users by their balance, for instance, to get only the users with a negative balance. Simply chaining ->where('balance', '<', 0); won’t work because balance isn’t a column in the database; it’s a computed column.

The Solution

The correct approach to filter based on a computed balance is to use the whereHas() method leading down to the transactions. Then, you can use havingRaw() to check the sum of the credit_movement. A working implementation looks like this:

Step-by-Step Implementation

Setting Up the Query: Use the whereHas method to filter on the relationship.

Summing the Credit Movement: Use select with a raw query to sum the credit_movement and alias it as balance.

Filtering with Having Clause: Finally, add a havingRaw condition to filter for balances less than zero.

Here’s how the final query would look:

[[See Video to Reveal this Text or Code Snippet]]

Why This Works

whereHas(): This method applies constraints on the existence of a relationship. Here, we are ensuring we only get users who have transactions, which is a necessary condition for calculating the balance.

select with SUM(): We are calculating the total credit_movement and assigning it the alias balance.

havingRaw(): This allows us to filter the results of the aggregate functions (like the sum) effectively, ensuring we only get results where the balance is less than zero.

Summary

To summarize, filtering users by a computed balance in Laravel Eloquent can initially seem complex, but using whereHas() combined with havingRaw() simplifies the process. By following the steps outlined in this guide, you can effectively filter users based on a condition applied to a sum of values in a related table.

Now you're equipped to manage such queries seamlessly in your Laravel applications! Happy coding!