Read-only data access objects

Read-only data access objects should 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 data access object of a read-only root collection:

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

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

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

SampleCollectionDao.prototype.fetchForInterval = function(connection, filter, callback) {
  // do something using connection and filter...
  // ...that produces the 'list' array for the given interval
  if (err)
    callback(err);
  else
    callback(null, list);
};

The synchronous version of the above example:

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

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

SampleCollectionDao.prototype.fetch = function(connection, filter) {
  // do something using connection and filter...
  // ...that produces the 'list' array
  return list;
};

SampleCollectionDao.prototype.fetchForInterval = function(connection, filter) {
  // do something using connection and filter...
  // ...that produces the 'list' array for the given interval
  return list;
};

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 data access object of a composite read-only 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 read-only 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;
};