Implement objection in water-abstraction-system (#34)

https://eaflood.atlassian.net/browse/WATER-3829

Implement [Objection ORM](https://www.npmjs.com/package/objection) in `water-abstraction-system`.

The time for running raw Knex queries is ending. We’ll be creating `billing_batches` and `events` soon. So, we need our chosen ORM in place to do this.

app/models/base.model.js

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+'use strict'
+
+/**
+ * @module BaseModel
+ */
+
+const { Model } = require('objection')
+
+const { db } = require('../../db/db.js')
+
+// We only have to do this once in the app and then it will be set globally for Objection. As we are not using multiple
+// databases we have no need to pass it into each query we build. And setting it here means all subclasses will inherit
+// it. https://vincit.github.io/objection.js/api/model/static-methods.html#static-knex
+Model.knex(db)
+
+class BaseModel extends Model {
+  /**
+   * An objective property we override to tell it where to search for models for relationships
+   *
+   * When setting a relationship in a model we have to provide a reference to the related model. As we need to set the
+   * relationship on both sides this leads to
+   * {@link https://vincit.github.io/objection.js/guide/relations.html#require-loops|require-loops}. We can avoid this
+   * by having the model tell Objection where to search for models for relationships. In the relationship declaration we
+   * can then just use a string value
+   *
+   * ```
+   *  // ...
+   *  relation: Model.ManyToManyRelation,
+        modelClass: 'charge_version.model',
+      // ...
+      ```
+
+      We don't want to do this in every model so set it in the `BaseModel` as Objection recommends.
+   */
+  static get modelPaths () {
+    return [__dirname]
+  }
+}
+
+module.exports = BaseModel

app/models/charge_version.model.js

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+'use strict'
+
+/**
+ * @module ChargeVersionModel
+ */
+
+const { Model } = require('objection')
+
+const BaseModel = require('./base.model.js')
+
+class ChargeVersionModel extends BaseModel {
+  static get tableName () {
+    return 'water.chargeVersions'
+  }
+
+  static get relationMappings () {
+    return {
+      licences: {
+        relation: Model.BelongsToOneRelation,
+        modelClass: 'licence.model',
+        join: {
+          from: 'water.charge_versions.licence_id',
+          to: 'water.licences.licence_id'
+        }
+      }
+    }
+  }
+}
+
+module.exports = ChargeVersionModel

app/models/licence.model.js

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+'use strict'
+
+/**
+ * @module LicenceModel
+ */
+
+const { Model } = require('objection')
+
+const BaseModel = require('./base.model.js')
+
+class LicenceModel extends BaseModel {
+  static get tableName () {
+    return 'water.licences'
+  }
+
+  static get relationMappings () {
+    return {
+      chargeVersions: {
+        relation: Model.HasManyRelation,
+        modelClass: 'charge_version.model',
+        join: {
+          from: 'water.licences.licence_id',
+          to: 'water.charge_versions.licence_id'
+        }
+      },
+      regions: {
+        relation: Model.BelongsToOneRelation,
+        modelClass: 'region.model',
+        join: {
+          from: 'water.licences.region_id',
+          to: 'water.regions.region_id'
+        }
+      }
+    }
+  }
+}
+
+module.exports = LicenceModel

app/models/region.model.js

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+'use strict'
+
+/**
+ * @module RegionModel
+ */
+
+const { Model } = require('objection')
+
+const BaseModel = require('./base.model.js')
+
+class RegionModel extends BaseModel {
+  static get tableName () {
+    return 'water.regions'
+  }
+
+  static get relationMappings () {
+    return {
+      licences: {
+        relation: Model.BelongsToOneRelation,
+        modelClass: 'licence.model',
+        join: {
+          from: 'water.regions.region_id',
+          to: 'water.licences.region_id'
+        }
+      }
+    }
+  }
+}
+
+module.exports = RegionModel

test/models/charge_version.model.test.js

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+'use strict'
+
+// Test framework dependencies
+const Lab = require('@hapi/lab')
+const Code = require('@hapi/code')
+
+const { describe, it } = exports.lab = Lab.script()
+const { expect } = Code
+
+// Thing under test
+const ChargeVersion = require('../../app/models/charge_version.model')
+
+describe('ChargeVersion model', () => {
+  it('returns data', async () => {
+    const query = await ChargeVersion.query()
+
+    expect(query).to.exist()
+  })
+})

test/models/licence.model.test.js

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+'use strict'
+
+// Test framework dependencies
+const Lab = require('@hapi/lab')
+const Code = require('@hapi/code')
+
+const { describe, it } = exports.lab = Lab.script()
+const { expect } = Code
+
+// Thing under test
+const Licence = require('../../app/models/licence.model.js')
+
+describe('Licence model', () => {
+  it('returns data', async () => {
+    const query = await Licence.query()
+
+    expect(query).to.exist()
+  })
+})

test/models/region.model.test.js

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+'use strict'
+
+// Test framework dependencies
+const Lab = require('@hapi/lab')
+const Code = require('@hapi/code')
+
+const { describe, it } = exports.lab = Lab.script()
+const { expect } = Code
+
+// Thing under test
+const Region = require('../../app/models/region.model')
+
+describe('Region model', () => {
+  it('returns data', async () => {
+    const query = await Region.query()
+
+    expect(query).to.exist()
+  })
+})