refactor(mapper): use object instead of class

BREAKING CHANGE: CustomMapper decorator no longer accepts classes but an object with the two methods
fromDb/toDb

Author: mumenthalers

README.md

@@ -109,6 +109,7 @@ Simple Type (no decorators required to work)
 - Boolean
 - Null
 - Array
+- String/Number Enum
 
 Complex Types (properties with these types need some decorators to work properly)
 - Set<simpleType | complexType>
@@ -130,7 +131,8 @@ Complex Types (properties with these types need some decorators to work properly
 | Date          | Not Supported |
 
 ## Custom Attribute Mapping
-It is always possible to define a custom mapping strategy, just implement the [MapperForType](https://shiftcode.github.io/dynamo-easy/interfaces/_mapper_for_type_base_mapper_.mapperfortype.html) class.
+It is always possible to define a custom mapping strategy, 
+just implement the [MapperForType](https://shiftcode.github.io/dynamo-easy/interfaces/_mapper_for_type_base_mapper_.mapperfortype.html) and provide with the CustomMapper directive.
 
 ## Collection Mapping (Array & Set)
 
@@ -152,39 +154,38 @@ We only support the native Date type and you need to explicitly mark a property
 (which is basically just syntactic sugar for @CustomMapper(TheDateMapper)).\
 If you want to use a different type for the @Date decorator (eg. Moment) you need to define a custom mapper and provide it to the dynamo easy config like this:\
 `updateDynamoEasyConfig({ dateMapper: MomentMapper })`\
--> Update the config before importing any models!
 
 
 A mapper for moment dates could look like this:
 ```typescript
 import * as moment from 'moment'
 import { MapperForType, StringAttribute } from '@shiftcoders/dynamo-easy'
 
-export class MomentMapper implements MapperForType<moment.Moment, StringAttribute> {
+export const MomentMapper: MapperForType<moment.Moment, StringAttribute> = {
 
-  fromDb(value: StringAttribute): moment.Moment {
-    const parsed: moment.Moment = moment(value.S, moment.ISO_8601)
+  fromDb: (value: StringAttribute) => {
+    const parsed = moment(value.S, moment.ISO_8601)
     if (!parsed.isValid()) {
       throw new Error(`the value ${value} cannot be parsed into a valid moment date`)
     }
     return parsed
-  }
+  },
 
-  toDb(value: moment.Moment): StringAttribute {
+  toDb: (value: moment.Moment) => {
     if (!moment.isMoment(value)) {
       throw new Error(`the value ${value} is not of type moment`)
     }
     if (!value.isValid()) {
       throw new Error(`cannot map property value ${value}, because it is not a valid moment date`)
     }
     return { S: value.clone().utc().format() }
-  }
+  },
 }
 ```
 
 
 ## Enum
-Enum values are persisted as Numbers (index of enum).
+Enum values are persisted as Numbers (index of enum) or string if string value was given.
 
 # Request API
 To start making requests create an instance of [DynamoStore](https://shiftcode.github.io/dynamo-easy/classes/_dynamo_dynamo_store_.dynamostore.html) and execute the desired operation using the provided api.
@@ -196,7 +197,8 @@ We support the following dynamodb operations with a fluent api:
 - Delete
 - Scan
 - Query
-- BatchGet
+- BatchGet (from a single table)
+- BatchWrite (to a single table)
 - MakeRequest (generic low level method for special scenarios)
 
 There is always the possibility to access the Params object directly to add values which are not covered with our api.