Add db.read()

Author: typicode

README.md

@@ -161,19 +161,22 @@ low('db.json', {
 })
 ```
 
-Full method signature:
+You can also define custom storages and formats:
 
 ```js
-low(source, {
-  storage: {
-    read: (source, deserialize) => // obj or a Promise
-    write: (dest, obj, serialize) => // undefined or a Promise
-  },
+const myStorage = {
+  read: (source, deserialize) => // obj or a Promise
+  write: (dest, obj, serialize) => // undefined or a Promise
+}
+
+const myFormat = {
   format: {
     deserialize: (data) => // obj
     serialize: (obj) => // data
   }
-}, writeOnChange)
+}
+
+low(source, { storage: myStorage, format: myFormat }, writeOnChange)
 ```
 
 __db.___
@@ -213,12 +216,24 @@ db.write()
 
 __db.write([source])__
 
-Persists database using `storage.write` method.
+Persists database using `storage.write` method. Depending on the storage, it may return a promise.
+
+Note: by default, lowdb automatically calls it when database changes.
 
 ```js
-const db = low('db.json')
-db.write()             // writes to db.json
-db.write('copy.json')  // writes to copy.json
+const db = low('db.json', { storage })
+db.write()            // writes to db.json
+db.write('copy.json') // writes to copy.json
+```
+
+__db.read([source])__
+
+Reads source using `storage.read` method. Depending on the storage, it may return a promise.
+
+```js
+const db = low('db.json', { storage })
+db.read()            // re-reads db.json
+db.read('copy.json') // reads copy.json
 ```
 
 ## Guide

src/index.js

@@ -35,10 +35,26 @@ function low (source, options = {}, writeOnChange = true) {
   if (source) {
     if (options.storage) {
       const { storage } = options
-      db.read = storage.read
-      db.write = storage.write
-        ? (dest = source) => storage.write(dest, db.object, db.serialize)
-        : null
+
+      if (storage.read) {
+        db.read = (s = source) => {
+          const res = storage.read(s, db.deserialize)
+
+          if (isPromise(res)) {
+            return res.then((obj) => {
+              db.object = obj
+              return db
+            })
+          }
+
+          db.object = res
+          return db
+        }
+      }
+
+      if (storage.write) {
+        db.write = (dest = source) => storage.write(dest, db.object, db.serialize)
+      }
     }
 
     options.format && Object.assign(db, options.format)
@@ -81,19 +97,11 @@ function low (source, options = {}, writeOnChange = true) {
   db.source = source
 
   // Init
-  if (db.source && db.read) {
-    const res = db.read(db.source, db.deserialize)
-    if (isPromise(res)) {
-      return res.then((obj) => {
-        db.object = obj
-        return db
-      })
-    } else {
-      db.object = res
-    }
+  if (db.read) {
+    return db.read(source)
+  } else {
+    return db
   }
-
-  return db
 }
 
 module.exports = low

test/index.js

@@ -64,6 +64,22 @@ const _test = (str, { source, read, write, promise, writeOnChange} = {}) => {
         t.same(args, ['backup.json', {}, undefined])
       }
 
+      if (read) {
+        // Read
+        promise
+          ? await db.read()
+          : db.read()
+
+        t.is(read.callCount, 2)
+
+        promise
+          ? await db.read('backup.json')
+          : db.read('backup.json')
+
+        let args = read.args.slice(-1)[0]
+        t.same(args, ['backup.json', undefined])
+      }
+
       t.end()
     } catch (err) {
       t.end(err)