Let us compare this newfangled "auto-mobile" invention to my favorite form of transportation, the horse: Where would you mount your favorite riding saddle on an auto-mobile?
This is nice, and as others have noted there are similar APIs that can be used with SQL. But I find it bad practice to extend arbitrary queries with additional conditions. This is very likely to lead to poor performance and perhaps correctness problems. In practice you need to have more semantic understanding of your query, so having an opaque 'query' object is no more helpful than a SQL string.
I believe army's point was that when using an SQL query builder API, one does not start with a string, but something which allows them to do a similar check that you showed.
I'm also not sure how your comment replies to army's point. The point, as I understood it, is that it is not accurate to characterize SQL queries as steps that tell the engine what to do. SQL is declarative, and leaves the execution plan up to the database itself. army's comments about the API and strings were trying to point out the only perceived difference, which is not relevant to the question of declarative versus imperative.
"You already have an existing ReQL query in a string variable. You need to add the age > 20 condition to that query."
Same problem. Comparing apples and oranges, strings and some "live" code. If you put ReQL and SQL into the same category (either as a string or as a thing that represents some "live" running code that you can manipulate at runtime) then it is difficult for me, at least, to really grasp what the differences are between them. SQL is certainly not considered an imperative language, eh?
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EDIT to respond to the comments below from TylerE and pests:
Oh but you do have ReQL as a string: when you type it into the editor, when it lives on disk as a file of source code. At some point that code becomes live and you can interact with it. The exact same basic transformation happens whether the syntax is ReQL or SQL, just in different ways and at different times depending on how you choose to run it not what syntax it's in. The issues are orthogonal and it certainly fair to demand that we compare the right things.
If you want to say that ReQL is a better syntax than SQL, well, I don't see it (yet.)
If you want to say that the product in question provides a nice way to run ReQL syntax queries in some fashion that is fundamentally better than the way that some other product allows you to run SQL queries, that is a whole different issue (and NOT the one I am addressing in my comment above.)
No it's not. Because there is no such thing as a ReQL query in a string. It's an object, usually built by chain methods. There is no textual representation.
Edit to your edit: It seems you are fundamentally not getting it. The ReQL is live code in your native programming environment. That means you can inspect it and manipulate it. SQL doesn't get interpreted (or whatever, it's black box) until it hits the server.
Imagine you're in a world where there are no XML parsing libraries. SQL is a string containing XML. ReQL is a DOM object.
You are a comparing a language (SQL is independent to the language you're programming with) to an API.
RethinkDB has API available for three languages: JavaScript, Python & Ruby. If you take look carefully while it tries to be consistent across them, there are still parts that are specific to given language. If you would want to use RethinkDB with a language that is completely different (for example a functional language), assuming RethinkDB would support it, you're guaranteed that the interaction with the DB would be completely different, while you could still use the same SQL language[1].
If you want to compare RethinkDB's API to something similar you should compare it with something like JOOQ[2].
Just to preemptively respond to argument about translating DSL to SQL. Currently modern driver communicates with database using binary protocol, the SQL is compiled on client side. You could actually skip SQL altogether, but then you would lose flexibility of being able to support many other databases.
Try to understand the context in which what I am saying makes sense, it will blow your mind and make you a better programmer when you do.
(Expanding upon that: We are both correct but not in the same context. There's a context in which what you are saying is true and sensible, and there is another context wherein what I am saying is true and sensible. I can switch between the contexts, so I am not trying to disagree with you, I am trying to give you data to help you to understand this other context and switch between then too. Additionally, this other context is of a higher "logical level" in the mathematical sense than the one we already have in common, and so when you do grok it I can confidently predict both that it with blow you mind and improve your ability to write software.)
Then it's not a string, it's a ReQL query object. Same way a Django model instance isn't a string. Your comparison seems way too artificially made up towards Rethink, so much so that it discredits itself.
Imagine me saying "here's a SQL string, let's see which database can execute it more easily, Rethink or Postgres. Hint: Start with writing a parser to convert it to ReQL".
The challenge is to make sure the column/field `age` is more than 20.
My code is:
What's yours? (Hint: start by writing a compliant SQL parser)