Create transaction model (#79)

As part of the work to implement a "add transaction to bill run" endpoint, this change creates a migration to create the transactions table in the database, creates a transaction model which has a relationship with the bill run model, and updates the bill run model to reflect this relationship.

app/models/bill_run.model.js

@@ -29,6 +29,14 @@ class BillRunModel extends BaseModel {
           from: 'bill_runs.regime_id',
           to: 'regimes.id'
         }
+      },
+      transactions: {
+        relation: Model.HasManyRelation,
+        modelClass: 'transaction.model',
+        join: {
+          from: 'bill_runs.id',
+          to: 'transactions.bill_run_id'
+        }
       }
     }
   }

app/models/transaction.model.js

@@ -0,0 +1,29 @@
+'use strict'
+
+/**
+ * @module TransactionModel
+ */
+
+const { Model } = require('objection')
+const BaseModel = require('./base.model')
+
+class TransactionModel extends BaseModel {
+  static get tableName () {
+    return 'transactions'
+  }
+
+  static get relationMappings () {
+    return {
+      billRun: {
+        relation: Model.BelongsToOneRelation,
+        modelClass: 'bill_run.model',
+        join: {
+          from: 'transactions.bill_run_id',
+          to: 'bill_runs.id'
+        }
+      }
+    }
+  }
+}
+
+module.exports = TransactionModel

db/migrations/20201203144442_create_transactions.js

@@ -0,0 +1,34 @@
+'use strict'
+
+const tableName = 'transactions'
+
+exports.up = async function (knex) {
+  await knex
+    .schema
+    .createTable(tableName, table => {
+      // Primary Key
+      table.uuid('id').primary().defaultTo(knex.raw('gen_random_uuid()'))
+
+      // Data
+      table.uuid('bill_run_id').notNullable()
+      table.integer('charge_value').notNullable()
+      table.boolean('charge_credit').notNullable()
+
+      // Automatic timestamps
+      table.timestamps(false, true)
+    })
+
+  await knex.raw(`
+    CREATE TRIGGER update_timestamp
+    BEFORE UPDATE
+    ON ${tableName}
+    FOR EACH ROW
+    EXECUTE PROCEDURE update_timestamp();
+  `)
+}
+
+exports.down = async function (knex) {
+  return knex
+    .schema
+    .dropTableIfExists(tableName)
+}