Editable data access objects - fetch() method

• Editable data access objects
• create() method
• fetch() method
• insert() method
• update() method
• remove() method

Root editable data access objects usually have a fetch() method, and optionally its alternate methods. It has the hereunder arguments:

• connection
  An object with connection information to the store. It depends on the persistence procedure.
• filter
  An optional object that contains the filter criteria of the data retrieval.
• callback
  For asynchronous objects: A function with callback(err, result) signature, where err is the eventual error and result is an optional return object of the retrieval. The properties of the return object hold the values of the properties of the instance.
• returns
  For synchronous objects: An optional object that holds the result of the retrieval.

The following code snippet shows a sample fetch() method of a root editable data access object:

var util = require('util');
var bo = require('business-objects');

var SampleRootDao = function() {
  SampleRootDao.super_.call(this, 'SampleCollectionDao');
};
util.inherits(SampleRootDao, bo.dataAccess.DaoBase);

SampleRootDao.prototype.fetch = function(connection, filter, callback) {
  // do something using connection and filter...
  // ...that produces the 'data' object
  if (err)
    callback(err);
  else
    callback(null, data);
};

SampleRootDao.prototype.fetchByName = function(connection, filter, callback) {
  // do something using connection and filter...
  // ...that produces the 'data' object for the given name
  if (err)
    callback(err);
  else
    callback(null, data);
};

The synchronous version of the above example:

var util = require('util');
var bo = require('business-objects');

var SampleRootDao = function() {
  SampleRootDao.super_.call(this, 'SampleCollectionDao');
};
util.inherits(SampleRootDao, bo.dataAccess.DaoBase);

SampleRootDao.prototype.fetch = function(connection, filter) {
  // do something using connection and filter...
  // ...that produces the 'data' object
  return data;
};

SampleRootDao.prototype.fetchByName = function(connection, filter) {
  // do something using connection and filter...
  // ...that produces the 'data' object for the given name
  return data;
};

The root objects are supposed to retrieve the data of the child objects as well. The purpose of this solution is to accelerate the construction of business objects by reducing the number of required connections to the data store.

The following is an example fetch() method of a data access object of a composite root editable object:

var util = require('util');
var bo = require('business-objects');

function fetchItems(connection, parentKey, callback) {
  // do something using connection and parentKey...
  // ...that produces the 'items' array
  if (err)
    callback(err);
  else
    callback(null, items);
}

var SampleRootDao = function() {
  SampleRootDao.super_.call(this, 'SampleRootDao');
};
util.inherits(SampleRootDao, bo.dataAccess.DaoBase);

SampleRootDao.prototype.fetch = function(connection, filter, callback) {
  // do something using connection and filter...
  // ...that produces the 'data' object
  if (err) {
    callback(err);
    return;
  }
  fetchItems(connection, data.key, function(err, items) {
    if (err)
      callback(err);
    else {
      // items: the name of the property that holds the child model or collection
      data.items = items;
      callback(null, data);
    }
  };
};

The synchronous version of the composite editable example:

var util = require('util');
var bo = require('business-objects');

function fetchItems(connection, parentKey) {
  // do something using connection and parentKey...
  // ...that produces the 'items' array
  return items;
}

var SampleRootDao = function() {
  SampleRootDao.super_.call(this, 'SampleRootDao');
};
util.inherits(SampleRootDao, bo.dataAccess.DaoBase);

SampleRootDao.prototype.fetch = function(connection, filter, callback) {
  // do something using connection and filter...
  // ...that produces the 'data' object
  // items: the name of the property that holds the child model or collection
  data.items = fetchItems(connection, data.key);
  return data;
};