feat(database): add aggregation helpers

* rowsCount

* Aggregates - static model count

* spacing fix

* Finalize aggregates

* rename to get

* typo

* Move to Database layer

* formatting fix

* formatting fix

* Knex refactor

* Standard styling

* Fix QueryBuilder proxy chaining

* add distinct aggregates

* Add distinct tests and fix typos

* refactor(database): refactor code style

* refactor(lucid): add aggregates to model query builder

* Revert "Fix QueryBuilder proxy chaining"

This reverts commit b5ea8a7.

* Added distinct helpers to QueryBuilder

* Revert "Added distinct helpers to QueryBuilder"

This reverts commit dd164aa.

* Revert "Revert "Fix QueryBuilder proxy chaining""

This reverts commit 4a30f68.

* Added database test to clarify the need for query wrapping

* fix(querybuilder): use new query instance over clone

* fix: Added aggregate helper support to BelongsToMany and fixed aggregate query column selection bug

re #225 re #205

* fix(Removed _prepareAggregate (unneeded)):

re #205 re #226

* style(Spelling fix):

* Testing fix

* Remove old comment

src/Database/MonkeyPatch.js

@@ -131,6 +131,140 @@ KnexQueryBuilder.prototype.paginate = async function (page = 2, perPage = 20) {
   }
 }
 
+/**
+ * Generates an aggregate function, that returns the aggregated result
+ * as a number.
+ *
+ * @method generateAggregate
+ *
+ * @param  {String}          aggregateOp
+ * @param  {String}          defaultColumnName
+ *
+ * @return {Number}
+ *
+ * @example
+ * ```js
+ * generateAggregate('count')
+ * ```
+ */
+function generateAggregate (aggregateOp, defaultColumnName = undefined) {
+  let funcName = `get${_.upperFirst(aggregateOp)}`
+
+  /**
+   * Do not re-add the method if exists
+   */
+  if (KnexQueryBuilder.prototype[funcName]) {
+    return
+  }
+
+  KnexQueryBuilder.prototype[funcName] = async function (columnName = defaultColumnName) {
+    if (!columnName) {
+      throw new Error(`'${funcName}' requires a column name.`)
+    }
+
+    const wrapper = new this.constructor(this.client)
+    const query = wrapper.from(this.as('__lucid'))[aggregateOp](`${columnName} as __lucid_aggregate`)
+    const results = await query
+    return results[0].__lucid_aggregate
+  }
+}
+
+/**
+ * Fetch and return a row count
+ *
+ * @method getCount
+ * @async
+ *
+ * @param  {String}   columnName = '*'
+ *
+ * @return {Number} The count of of rows in this query
+ */
+generateAggregate('count', '*')
+
+/**
+ * Fetch and return a distinct row count
+ *
+ * @method getCountDistinct
+ * @async
+ *
+ * @param  {String}   columnName
+ *
+ * @return {Number} The distinct count of rows in this query
+ */
+generateAggregate('countDistinct')
+
+/**
+ * Fetch and return the sum of all values in columnName
+ *
+ * @method getSum
+ * @async
+ *
+ * @param  {String}   columnName
+ *
+ * @return {Number} The sum of columnName
+ */
+generateAggregate('sum')
+
+/**
+ * Fetch and return the sum of all distinct values in columnName
+ *
+ * @method getSumDistinct
+ * @async
+ *
+ * @param  {String}   columnName
+ *
+ * @return {Number} The sum of distinct values in columnName
+ */
+generateAggregate('sumDistinct')
+
+/**
+ * Fetch and return the minimum of all values in columnName
+ *
+ * @method getMin
+ * @async
+ *
+ * @param  {String}   columnName
+ *
+ * @return {Number} The minimunm value of columnName
+ */
+generateAggregate('min')
+
+/**
+ * Fetch and return the maximum of all values in columnName
+ *
+ * @method getMax
+ * @async
+ *
+ * @param  {String}   columnName
+ *
+ * @return {Number} The maximunm value of columnName
+ */
+generateAggregate('max')
+
+/**
+ * Fetch and return the average of all values in columnName
+ *
+ * @method getAvg
+ * @async
+ *
+ * @param  {String}   columnName
+ *
+ * @return {Number} The average value of columnName
+ */
+generateAggregate('avg')
+
+/**
+ * Fetch and return the average of all distinct values in columnName
+ *
+ * @method getAvgDistinct
+ * @async
+ *
+ * @param  {String}   columnName
+ *
+ * @return {Number} The average of distinct values of columnName
+ */
+generateAggregate('avgDistinct')
+
 /**
  * Returns the latest row from the database.
  *

src/Lucid/Model/index.js

@@ -1327,6 +1327,109 @@ class Model extends BaseModel {
       this.newUp(newInstance.$attributes)
     }
   }
-}
 
+ /**
+  * Return a count of all model records.
+  *
+  * @method getCount
+  *
+  * @param  {String} columnName = '*'
+  *
+  * @return {Number}
+  */
+  static async getCount (columnName = '*') {
+    return this.query().getCount(columnName)
+  }
+
+  /**
+  * Return a distinct count of all model records.
+  *
+  * @method getCountDistinct
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  static async getCountDistinct (columnName) {
+    return this.query().getCountDistinct(columnName)
+  }
+
+ /**
+  * Return the average of all values of columnName.
+  *
+  * @method getAvg
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  static async getAvg (columnName) {
+    return this.query().getAvg(columnName)
+  }
+
+  /**
+  * Return the average of all distinct values of columnName.
+  *
+  * @method getAvgDistinct
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  static async getAvgDistinct (columnName) {
+    return this.query().getAvgDistinct(columnName)
+  }
+
+ /**
+  * Return the minimum of all values of columnName.
+  *
+  * @method getMin
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  static async getMin (columnName) {
+    return this.query().getMin(columnName)
+  }
+
+ /**
+  * Return the maximum of all values of columnName.
+  *
+  * @method getMax
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  static async getMax (columnName) {
+    return this.query().getMax(columnName)
+  }
+
+ /**
+  * Return the sum of all values of columnName.
+  *
+  * @method getSum
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  static async getSum (columnName) {
+    return this.query().getSum(columnName)
+  }
+
+ /**
+  * Return the sum of all distinct values of columnName.
+  *
+  * @method getSumDistinct
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  static async getSumDistinct (columnName) {
+    return this.query().getSumDistinct(columnName)
+  }
+}
 module.exports = Model

src/Lucid/QueryBuilder/index.js

@@ -444,6 +444,110 @@ class QueryBuilder {
     return new this.Model.Serializer(modelInstances, pages)
   }
 
+ /**
+  * Return a count of all model records.
+  *
+  * @method getCount
+  *
+  * @param  {String} columnName = '*'
+  *
+  * @return {Number}
+  */
+  getCount (columnName = '*') {
+    return this.query.getCount(columnName)
+  }
+
+  /**
+  * Return a distinct count of all model records.
+  *
+  * @method getCountDistinct
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  getCountDistinct (columnName) {
+    return this.query.getCountDistinct(columnName)
+  }
+
+ /**
+  * Return the average of all values of columnName.
+  *
+  * @method getAvg
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  getAvg (columnName) {
+    return this.query.getAvg(columnName)
+  }
+
+  /**
+  * Return the average of all distinct values of columnName.
+  *
+  * @method getAvgDistinct
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  getAvgDistinct (columnName) {
+    return this.query.getAvgDistinct(columnName)
+  }
+
+  /**
+  * Return the minimum of all values of columnName.
+  *
+  * @method getMin
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  getMin (columnName) {
+    return this.query.getMin(columnName)
+  }
+
+  /**
+  * Return the maximum of all values of columnName.
+  *
+  * @method getMax
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  getMax (columnName) {
+    return this.query.getMax(columnName)
+  }
+
+ /**
+  * Return the sum of all values of columnName.
+  *
+  * @method getSum
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  getSum (columnName) {
+    return this.query.getSum(columnName)
+  }
+
+ /**
+  * Return the sum of all distinct values of columnName.
+  *
+  * @method getSumDistinct
+  *
+  * @param  {String} columnName
+  *
+  * @return {Number}
+  */
+  getSumDistinct (columnName) {
+    return this.query.getSumDistinct(columnName)
+  }
+
   /**
    * Bulk update data from query builder. This method will also
    * format all dates and set `updated_at` column

src/Lucid/Relations/BaseRelation.js

@@ -15,10 +15,22 @@ const proxyGet = require('../../../lib/proxyGet')
 const methodsList = [
   'increment',
   'decrement',
+  'sum',
+  'sumDistinct',
   'avg',
+  'avgDistinct',
   'min',
   'max',
   'count',
+  'countDistinct',
+  'getSum',
+  'getSumDistinct',
+  'getAvg',
+  'getAvgDistinct',
+  'getMin',
+  'getMax',
+  'getCount',
+  'getCountDistinct',
   'truncate',
   'ids',
   'paginate',