fogine/couchbase-odm

To create custom key generation strategy your constructor function must include `require('kouchbase-odm').Key.prototype` in its prototype chain.  
See {@link Key Key API Reference} for details about abstract methods and methods which may be overriden.

````javascript
    const util         = require('util');
    const couchbaseODM = require('kouchbase-odm');
    const Key          = couchbaseODM.Key;

    /*
     * constructor
     *
     * the constructor will be called with options which were set when defining
     * a Model (or CouchbaseODM instance)
     * @param {Object}         options
     * @param {string|integer} options.id
     * @param {string}         options.prefix=defaults to Model's name
     * @param {string}         options.postfix=""
     * @param {string}         options.delimiter="_"
     */
    function UUID1Key(options) {
        Key.call(this, options);
    }

    //every key generation strategy must expose static `dataType` property
    // which determines data type of document's `id`. Usually it will be
    // `string` or `integer`
    UUID1Key.dataType = 'string';

    //behavior delegation - adds `Key.prototype` to `UUID1Key`'s prototype chain
    util.inherits(UUID1Key, Key);

    /**
     * generate
     *
     * generates new key
     * The method must return a prosime with generated `Key` object (self)
     *
     * @param {Instance} instance - document object
     * @return {Promise<UUID1Key>}
     */
    UUID1Key.prototype.generate = function(instance) {
        const id = uuid.v1();
        this.setId(id); //see Key.setId for more information
        return Promise.resolve(this);
    };
````

the `generate` method is always run with document object ({@link Instance}) the key is generated for.  

The above example just generates custom id value (dynamic part of a key of a document). You could take control over whole key string format by overriding the [toString](https://github.com/fogine/couchbase-odm/blob/master/lib/key/key.js#L154) method of the `Key` prototype.

### Using custom Key

So now when you've created the custom generation strategy you can use it simply like:  

````javascript
    const User = couchbase.define('User', {
        type: 'object'
    }, {
        //options object
        key: UUID1Key  // ==> provide constructor function object as the option when defining a Model
    });
````


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**NOTE:** The same procedure applies for providing custom key generation strategy of reference document keys (`refDocKey` option on a Model)