Coincap FDW

This is just an idea of how one could write a Foreign data wrapper in hy.

Honestly I don't think the code is ideal but it shows you how to init the subclass considering the required parameters from the superclass.

Also, it is great to be able to use a lisp dialect to achieve this.

If you want to fork this and implement additional things like INSERT, UPDATE and DELETE support or even COMMIT, ROLLBACK you should take a look at the Multicorn tutorial. It should be very straightforward.

It wouldn't make sense to have these methods for a read only API, but I might try to create another FDW at some point that might have them.

Usage

1. After installing multicorn, you should be able to just install this fdw using pip:

pip3 install coincap-fdw

2. Then you need to make sure you've created the extension within the postgres db:

CREATE EXTENSION multicorn;

3. You should be able to create the server. You can name it however you want, in this case I'm calling it coincap:

CREATE SERVER coincap
    FOREIGN DATA WRAPPER multicorn
    options (wrapper 'coincap_fdw.CoinCapForeignDataWrapper');

4. You can create the table now. Any additional field you want (comming from the API), just add here as TEXT. You can also give any name to the table, in this case I'm calling it crypto_assets:

 CREATE FOREIGN TABLE crypto_assets (
    id TEXT,
    name TEXT,
    rank TEXT,
    symbol TEXT,
    priceusd TEXT,
    changepercent24hr TEXT,
    supply TEXT,
    volumeusd24hr TEXT
) server coincap;

5. After that, just run a query:

SELECT name,
       cast(priceusd AS float)
FROM crypto_assets
ORDER BY 2 DESC
LIMIT 10;

      name       |      priceusd
-----------------+--------------------
 Bitcoin BEP2    | 32172.540563633753
 Bitcoin         |  32161.39844805744
 Wrapped Bitcoin |  32142.40818287929
 yearn.finance   | 28157.691588592475
 Maker           | 2412.0048277811693
 Ethereum        |  2005.716450530913
 Bitcoin Cash    |   433.355437728395
 Compound        |  388.5222106608794
 Binance Coin    |  283.2426902826701
 Aave            |  270.9662792522684
(10 rows)