The Expense model represents a single expense transaction within a group. It tracks who paid, the amount, and how the expense should be split among group members.
Data Class Definition
package com.example.divvy.models
import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable
@Serializable
data class Expense(
val id: String = "",
@SerialName("group_id") val groupId: String = "",
val merchant: String = "",
@SerialName("amount_cents") val amountCents: Long = 0L,
@SerialName("split_method") val splitMethod: String = "EQUAL",
val currency: String = "USD",
@SerialName("paid_by_user_id") val paidByUserId: String = "",
@SerialName("created_at") val createdAt: String = ""
)
Fields
Unique identifier for the expense
ID of the group this expense belongs to. Serialized as group_id in JSON/database.
Name of the merchant or description of the expense (e.g., “Grocery Store”, “Dinner at Restaurant”)
Total amount of the expense in cents. Serialized as amount_cents in JSON/database.
splitMethod
String
default:"\"EQUAL\""
Method for splitting the expense among members. Common values:
"EQUAL" - Split evenly among all participants"PERCENTAGE" - Split by custom percentages"EXACT" - Split by exact amounts
Serialized as split_method in JSON/database. Three-letter ISO currency code for the transaction
User ID of the member who paid for the expense. Serialized as paid_by_user_id in JSON/database.
ISO timestamp when the expense was created. Serialized as created_at in JSON/database.
Serialization
The Expense model uses Kotlin Serialization with snake_case field names for database compatibility:
| Kotlin Property | JSON/Database Field |
|---|
groupId | group_id |
amountCents | amount_cents |
splitMethod | split_method |
paidByUserId | paid_by_user_id |
createdAt | created_at |
GroupExpense
For a more comprehensive expense model with split details, see GroupExpense. The GroupExpense model extends Expense with:
- Detailed split information per user
title field instead of merchant- List of
ExpenseSplit objects
ExpenseSplit
From [GroupExpense.kt]:
@Serializable
data class ExpenseSplit(
@SerialName("user_id") val userId: String,
@SerialName("amount_cents") val amountCents: Long,
@SerialName("is_covered_by") val isCoveredBy: String? = null
)
Split
A simpler split model used in some contexts:
@Serializable
data class Split(
val userId: String,
val amountCents: Long,
val coveredByUserId: String? = null
)
Usage Examples
Creating an Expense
val expense = Expense(
id = "exp_456",
groupId = "grp_123",
merchant = "Whole Foods",
amountCents = 8599L, // $85.99
splitMethod = "EQUAL",
currency = "USD",
paidByUserId = "user_abc",
createdAt = "2026-03-03T10:30:00Z"
)
Repository Operations
From [ExpensesRepository.kt]:
// List all expenses for a group
suspend fun listExpensesByGroup(groupId: String): List<Expense>
// Create a new expense
suspend fun createExpense(
groupId: String,
description: String,
amountCents: Long,
splitMethod: String
): GroupExpense
// Update an existing expense
suspend fun updateExpense(
expenseId: String,
description: String,
amountCents: Long,
splitMethod: String
)
// Delete an expense
suspend fun deleteExpense(expenseId: String)
Converting to GroupExpense
From [ExpensesRepository.kt:158]:
private fun Expense.toGroupExpense() = GroupExpense(
id = id,
groupId = groupId,
title = merchant,
amountCents = amountCents,
paidByUserId = paidByUserId,
splits = emptyList(),
createdAt = createdAt
)
Split Methods
Equal Split
From [GroupExpense.kt:30]:
/**
* Splits [amountCents] evenly across [userIds].
* Leftover cents (from integer division) are distributed one per person
* to the first members in the list.
*/
fun splitEqually(amountCents: Long, userIds: List<String>): List<ExpenseSplit> {
require(userIds.isNotEmpty()) { "userIds must not be empty" }
val base = amountCents / userIds.size
val remainder = (amountCents % userIds.size).toInt()
return userIds.mapIndexed { index, userId ->
ExpenseSplit(userId, if (index < remainder) base + 1 else base)
}
}
Percentage Split
From [GroupExpense.kt:44]:
/**
* Splits [amountCents] according to [percentages], a map of userId → share (0–100).
* Percentages must sum to 100 (±0.01 tolerance).
* Rounding uses the largest-remainder method so the splits always total exactly [amountCents].
*/
fun splitByPercentage(amountCents: Long, percentages: Map<String, Double>): List<ExpenseSplit>