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wonder95's avatar

Laravel model structure for breaking cost into categories

For a side project, I'm creating a small personal budgeting type app, and one of the features is basically an account register, where you can enter a payment to a vendor. Part of this is being able to categorize the payment - either as a whole, or spread across different categories. Say, for instance, that I go to Home Depot, and I buy stuff for my yard, and other stuff for some remodeling work in my house, so I want some to the Landscaping category, and some to Home Repair.

So for my relevant models, I have a Transaction model, and a SpendingCategory model.

Fields are:

  • Transaction - id, date, amount
  • SpendingCategory - name

So with all that, my issue is this; the best way to break the payment down into multiple categories with an amount. SpendingCategory is obviously just the definition of the category, so I can't have an amount field in it, because the amount will vary every time I use it. As best I can tell I need a third model, something like CategoryAmount with a relationship to Transaction that also has an amount field. So then, my Transaction model would have a categoryAmount relationship:

public function categoryAmount()
{
    return $this->hasMany(CategoryAmount::class);
}

and the inverse on CategoryAmount would be

public function transaction()
{
    return $this->belongsTo(Transaction::class);
}

For the relationships between CategoryAmount and SpendingCategory, my CategoryAmount model would have:

public function spendingCategory()
{
    return $this->belongsTo(SpendingCategory::class);
}

and the inverse on SpendingCategory would be

public function categoryAmount()
{
    return $this->hasMany(CategoryAmount::class);
}

So my spending_categories table would have transaction_id and spending_category_id columns, since it belongs to the Transaction and CategoryAmount tables.

Does that sound correct for what I'm trying to do, is is there a better set of relationships to use?

0 likes
11 replies
Tray2's avatar

It starts out ok, but you should not use a pivot for a one-to-many relation, just add the spending_category_id to the transaction.

wonder95's avatar

@Tray2 Well, it's not a pivot table, like in a many-to-many relationship, but like I said in the description, for each instance of a category assigned to a transaction, I also need to record the amount assigned to the spendingCategory. If I didn't need the amount, then I would do as you suggest.

wonder95's avatar

@Tray2 Yes, I have the total for the transaction. But, as I stated, I want to break down the total amount into smaller amounts by category, so a Transaction of $50 could have $30 assigned to CategoryA and $20 to CategoryB. That's why it's not so simple.

Tray2's avatar

@wonder95 Then you really should rethink your approach, it's better to keep the transactions seperate instead of first entering the total, and then define the items.

I would create a transaction for each, but have an identifier like receipt number to keep them together. It will give a simpler model with just two tables and a one-to-many relation between your transactions and the categories.

Snapey's avatar

terminology....

I would create a splits table and Split model containing transaction_id and category_id and amount

transaction has many splits, split belongs to transaction

category has many splits, split belongs to category

By not thinking of it as a pivot table makes its purpose clearer, and its name makes it clear what it is.

wonder95's avatar

@Snapey Actually, what you describe is - as I read it - basically what I have. The only difference is naming; what you call Splits is what I called CategoryAmount, and what you call Category I call SpendingCategory (I use that because elsewhere I have BudgetCategory). It would have category_id, transaction_id, and amount. I actually have that exact diagram on my notepad, and it looks like the way I have them defined above matches what you suggest.

I like the way you think. :-)

martinbean's avatar

@wonder95 I may be misunderstanding here, but can you not just add a category column to your transactions table? And then you just get the spend per category by grouping your transactions by category ID?

wonder95's avatar

@martinbean Well, no, because that would only allow one category per transaction, and my whole goal is to be able to split the amount of one transaction across multiple categories.

martinbean's avatar

@wonder95 In that case, make “categories” a many-to-many relation, but add an amount column to the pivot table in order to specify how much should be attributed to that category. But you’ll then need to add business logic in your application to ensure all categories’ amounts add up to exactly 100% of the transaction they’re related to.

LaryAI's avatar
LaryAI
AI
1 year ago
Level 58

Your proposed solution is on the right track, but there are a few clarifications and corrections needed to ensure the relationships and database structure are set up correctly.

Database Structure

  1. Transactions Table

    • id
    • date
    • amount (total amount of the transaction)

  2. SpendingCategories Table

    • id
    • name

  3. CategoryAmounts Table (This is the pivot table)

    • id
    • transaction_id (foreign key to Transactions)
    • spending_category_id (foreign key to SpendingCategories)
    • amount (amount allocated to this category for the transaction)

Model Relationships

  1. Transaction Model
class Transaction extends Model
{
    public function categoryAmounts()
    {
        return $this->hasMany(CategoryAmount::class);
    }
}
  1. CategoryAmount Model
class CategoryAmount extends Model
{
    public function transaction()
    {
        return $this->belongsTo(Transaction::class);
    }

    public function spendingCategory()
    {
        return $this->belongsTo(SpendingCategory::class);
    }
}
  1. SpendingCategory Model
class SpendingCategory extends Model
{
    public function categoryAmounts()
    {
        return $this->hasMany(CategoryAmount::class);
    }
}

Explanation

  • Transaction to CategoryAmount: A transaction can have multiple category amounts, hence the hasMany relationship.
  • CategoryAmount to Transaction: Each category amount belongs to a single transaction, hence the belongsTo relationship.
  • CategoryAmount to SpendingCategory: Each category amount is associated with a single spending category, hence the belongsTo relationship.
  • SpendingCategory to CategoryAmount: A spending category can be associated with multiple category amounts, hence the hasMany relationship.

Additional Considerations

  • Ensure that you have the necessary foreign key constraints in your database migrations for data integrity.
  • You might want to add validation logic to ensure that the sum of the amounts in CategoryAmounts for a transaction does not exceed the total amount in the Transactions table.

This setup should allow you to allocate parts of a transaction to different spending categories effectively.

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