orm: add initial pg support (#9827)

examples/database/psql/.gitignore

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+customer

examples/database/psql/customer.v

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+module main
+
+import pg
+
+const dash = '----------------------------------------------------------------'
+
+struct Customer {
+	id int
+	name string
+	nr_orders int
+	country string
+}
+
+fn main() {
+	/*db := pg.connect(pg.Config{
+		host: 'localhost' //'127.0.0.1'
+		user: 'postgres'
+		dbname: 'customerdb'
+	}) or {
+		println('failed to connect')
+		println(err)
+		return
+	}
+
+	nr_customers := db.select count from Customer
+	println('Total customers: $nr_customers')
+
+	// V syntax can be used to build queries
+	println(dash)
+	bg_country := 'Bulgaria'
+	bg_customers := db.select from Customer where country == bg_country  && id != 2
+	for customer in bg_customers {
+		println('$customer.country | $customer.id - $customer.name')
+	}
+
+	println(dash)
+	ru_customers := db.select from Customer where country == 'Russia'
+	for customer in ru_customers {
+		println('$customer.country | $customer.id - $customer.name')
+	}
+
+	// by adding `limit 1` we tell V that there will be only one object
+	println(dash)
+	existing := db.select from Customer where id == 1 limit 1 or { panic(err) }
+	println('Existing customer name: $existing.name')
+	println('Existing customer full information:')
+	println(existing)
+
+	println(dash)
+	q := Customer{}
+	// It's easy to handle queries that don't return any data
+	if anon := db.select from Customer where id == 12345 && name == q.name &&
+			nr_orders > q.nr_orders limit 1 {
+		println('Non existing customer name: $anon.name')
+	}
+	// Insert a new customer
+	nc := Customer{
+		name: 'John Doe'
+		nr_orders: 10
+	}
+	db.insert(nc)*/
+}
+
+

examples/database/psql/mydb.sql

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+--
+-- PostgreSQL database dump
+--
+
+-- Dumped from database version 9.5.19
+-- Dumped by pg_dump version 9.5.19
+
+SET statement_timeout = 0;
+SET lock_timeout = 0;
+SET client_encoding = 'UTF8';
+SET standard_conforming_strings = on;
+SELECT pg_catalog.set_config('search_path', '', false);
+SET check_function_bodies = false;
+SET xmloption = content;
+SET client_min_messages = warning;
+SET row_security = off;
+
+--
+-- Name: plpgsql; Type: EXTENSION; Schema: -; Owner: 
+--
+
+CREATE EXTENSION IF NOT EXISTS plpgsql WITH SCHEMA pg_catalog;
+
+
+--
+-- Name: EXTENSION plpgsql; Type: COMMENT; Schema: -; Owner: 
+--
+
+COMMENT ON EXTENSION plpgsql IS 'PL/pgSQL procedural language';
+
+
+SET default_tablespace = '';
+
+SET default_with_oids = false;
+
+--
+-- Name: customers; Type: TABLE; Schema: public; Owner: myuser
+--
+
+CREATE TABLE public.customers (
+    id integer NOT NULL,
+    name text DEFAULT ''::text,
+    nr_orders integer DEFAULT 0,
+    country text DEFAULT 'England'::text,
+    created_at timestamp without time zone DEFAULT now()
+);
+
+
+ALTER TABLE public.customers OWNER TO myuser;
+
+--
+-- Name: customers_id_seq; Type: SEQUENCE; Schema: public; Owner: myuser
+--
+
+CREATE SEQUENCE public.customers_id_seq
+    START WITH 1
+    INCREMENT BY 1
+    NO MINVALUE
+    NO MAXVALUE
+    CACHE 1;
+
+
+ALTER TABLE public.customers_id_seq OWNER TO myuser;
+
+--
+-- Name: customers_id_seq; Type: SEQUENCE OWNED BY; Schema: public; Owner: myuser
+--
+
+ALTER SEQUENCE public.customers_id_seq OWNED BY public.customers.id;
+
+
+--
+-- Name: id; Type: DEFAULT; Schema: public; Owner: myuser
+--
+
+ALTER TABLE ONLY public.customers ALTER COLUMN id SET DEFAULT nextval('public.customers_id_seq'::regclass);
+
+
+--
+-- Data for Name: customers; Type: TABLE DATA; Schema: public; Owner: myuser
+--
+
+COPY public.customers (id, name, nr_orders, country, created_at) FROM stdin;
+2	Pippi Långstrump	3	Bulgaria	2019-08-19 09:41:30.78888
+1	Bilbo Begins	11	Bulgaria	2019-08-19 09:40:31.396807
+3	Viktualia Rullgardina	0	Bulgaria	2019-08-19 09:42:52.723223
+4	Krusmynta Efraimsdotter	5	Bulgaria	2019-08-19 09:43:04.083209
+5	Ana Karenina	0	Russia	2019-08-20 15:41:50.244971
+7	Jiji Lolobridgida	0	Italy	2019-08-20 15:42:26.020113
+6	Viktor Savashkin	8	Russia	2019-08-20 15:42:07.213557
+\.
+
+
+--
+-- Name: customers_id_seq; Type: SEQUENCE SET; Schema: public; Owner: myuser
+--
+
+SELECT pg_catalog.setval('public.customers_id_seq', 1, true);
+
+
+--
+-- Name: customers_pkey; Type: CONSTRAINT; Schema: public; Owner: myuser
+--
+
+ALTER TABLE ONLY public.customers
+    ADD CONSTRAINT customers_pkey PRIMARY KEY (id);
+
+
+--
+-- Name: SCHEMA public; Type: ACL; Schema: -; Owner: postgres
+--
+
+REVOKE ALL ON SCHEMA public FROM PUBLIC;
+REVOKE ALL ON SCHEMA public FROM postgres;
+GRANT ALL ON SCHEMA public TO postgres;
+GRANT ALL ON SCHEMA public TO PUBLIC;
+
+
+--
+-- PostgreSQL database dump complete
+--
+