How Should Complex ReQL Queries be Composed? - rethinkdb

Question

Are there any best practices or ReQL features that that help with composing complex ReQL queries?
In order to illustrate this, imagine a fruits table. Each document has the following structure.
{
"id": 123,
"name": "name",
"colour": "colour",
"weight": 5
}
If we wanted to retrieve all green fruits, we might use the following query.
r
.db('db')
.table('fruits')
.filter({colour: 'green'})
However, in more complex cases, we might wish to use a variety of complex command combinations. In such cases, bespoke queries could be written for each case, but this could be difficult to maintain and could violate the Don't Repeat Yourself (DRY) principle. Instead, we might wish to write bespoke queries which could chain custom commands, thus allowing complex queries to be composed in a modular fashion. This might take the following form.
r
.db('db')
.table('fruits')
.custom(component)
The component could be a function which accepts the last entity in the command chain as its argument and returns something, as follows.
function component(chain)
{
return chain
.filter({colour: 'green'});
};
This is not so much a feature proposal as an illustration of the problem of complex queries, although such a feature does seem intuitively useful.
Personally, my own efforts in resolving this problem have involved the creation of a compose utility function. It takes an array of functions as its main argument. Each function is called, passed a part of the query chain, and is expected to return an amended version of the query chain. Once the iteration is complete, a composition of the query components is returned. This can be viewed below.
function compose(queries, parameters)
{
if (queries.length > 1)
{
let composition = queries[0](parameters);
for (let index = 1; index < queries.length; index++)
{
let query = queries[index];
composition = query(composition, parameters);
};
return composition;
}
else
{
throw 'Must be two or more queries.';
};
};
function startQuery()
{
return RethinkDB;
};
function filterQuery1(query)
{
return query.filter({name: 'Grape'});
};
function filterQuery2(query)
{
return query.filter({colour: 'Green'});
};
function filterQuery3(query)
{
return query.orderBy(RethinkDB.desc('created'));
};
let composition = compose([startQuery, filterQuery1, filterQuery2, filterQuery3]);
composition.run(connection);
It would be great to know whether something like this exists, whether there are best practises to handle such cases, or whether this is an area where ReQL could benefit from improvements.

Answer 1

In RethinkDB doc, they state it clearly: All ReQL queries are chainable
Queries are constructed by making function calls in the programming
language you already know. You don’t have to concatenate strings or
construct specialized JSON objects to query the database. All ReQL
queries are chainable. You begin with a table and incrementally chain
transformers to the end of the query using the . operator
You do not have to compose another thing which just implicit your code, which gets it more difficult to read and be unnecessary eventually.
The simple way is assign the rethinkdb query and filter into the variables, anytime you need to add more complex logic, add directly to these variables, then run() it when your query is completed
Supposing I have to search a list of products with different filter inputs and getting pagination. The following code is exposed in javascript (This is simple code for illustration only)
let sorterDirection = 'asc';
let sorterColumnName = 'created_date';
var buildFilter = r.row('app_id').eq(appId).and(r.row('status').eq('public'))
// if there is no condition to start up, you could use r.expr(true)
// append every filter into the buildFilter var if they are positive
if (escapedKeyword != "") {
buildFilter = buildFilter.and(r.row('name').default('').downcase().match(escapedKeyword))
}
// you may have different filter to add, do the same to append them into buildFilter.
// start to make query
let query = r.table('yourTableName').filter(buildFilter);
query.orderBy(r[sorterDirection](sorterColumnName))
.slice(pageIndex * pageSize, (pageIndex * pageSize) + pageSize).run();