feat(clear): add clear() method, safeguard remove()

Add new `clear()` method to remove all objects from the model. Safeguard `remove()` so that empty criteria will not remove all objects.

src/index.js

@@ -122,6 +122,11 @@ class Trilogy {
     return model.remove(criteria)
   }
 
+  clear (location) {
+    let model = checkModel(this, location)
+    return model.clear()
+  }
+
   count (location, criteria, options) {
     let [table, column] = location.split('.', 2)
     let model = checkModel(this, table)

src/model.js

@@ -1,7 +1,7 @@
 import * as types from './types'
 import * as helpers from './helpers'
 import * as enforcers from './enforcers'
-import { isArray, isString } from './util'
+import { isArray, isString, isObject } from './util'
 
 export default class Model {
   constructor (ctx, name, schema, options) {
@@ -155,12 +155,25 @@ export default class Model {
   }
 
   remove (criteria) {
+    if (!helpers.isValidWhere(criteria)) {
+      return Promise.resolve(0)
+    }
+
+    if (isObject(criteria) && !Object.keys(criteria).length) {
+      return Promise.resolve(0)
+    }
+
     let query = this.ctx.knex(this.name).del()
     query = helpers.buildWhere(query, criteria)
 
     return helpers.runQuery(this.ctx, query)
   }
 
+  clear () {
+    let query = this.ctx.knex(this.name).truncate()
+    return helpers.runQuery(this.ctx, query)
+  }
+
   count (column, criteria, options = {}) {
     if (!isString(column)) {
       options = criteria