How do I query PostgreSQL within GNAT CE 2019 - linux

Question

I am trying to query a PostgreSQL database using GNAT CE 2019. I have two tables in my database, car and person:
mydb1-# \dt
List of relations
Schema | Name | Type | Owner
--------+--------+-------+----------
public | car | table | postgres
public | person | table | postgres
(2 rows)
I would like to perfom a simple Select statement, when I perform this using psql in my terminal, this is what's returned:
mydb1=# SELECT * FROM Person;
person_uid | first_name | last_name | gender | email | date_of_birth | country_of_birth | car_uid
--------------------------------------+------------+------------+--------+------------------------------+---------------+------------------+--------------------------------------
75f5e55d-12b2-463e-93ff-1c921e44c3e1 | Audrie | Vasyukov | Female | avasyukovd6#domainmarket.com | 1988-11-24 | Guatemala |
9e3f7f90-6e9a-4f2d-ae4e-c852d819ed33 | Nefen | Philippard | Male | nphilippardd7#economist.com | 2006-11-08 | Russia |
ffad6113-2321-47c3-8e1d-b8bbe1f7ffa1 | Leonore | Garthland | Female | lgarthlandd8#furl.net | 1991-03-23 | Canada |
268c1977-a5cc-4794-9cdd-e0e4af7890b9 | Yank | Turfitt | Male | yturfittd9#exblog.jp | 1990-02-07 | China |
3c815fa3-74b9-493a-9466-f32010806b16 | Benn | Pawley | Male | bpawleyda#indiegogo.com | 2006-10-28 | Russia |
690fc9e9-309e-4d70-8dab-167653b99763 | Tod | Easen | Male | teasend4#php.net | 1990-08-24 | China | 5fa7490e-ba42-4a96-b806-097bbb16e30e
However, I would like to perform this from within GNAT CE 2019. This is how my main.adb file currently looks:
with GNATCOLL.SQL.Postgres; use GNATCOLL.SQL.Postgres;
with GNATCOLL.SQL.Exec; use GNATCOLL.SQL.Exec;
with GNATCOLL.VFS; use GNATCOLL.VFS;
with GNATCOLL.SQL.Inspect; use GNATCOLL.SQL.Inspect;
with GNATCOLL.SQL; use GNATCOLL.SQL;
procedure Main is
-- Datebase Description
--
DB_Descr : GNATCOLL.SQL.Exec.Database_Description;
-- Database Connection
--
DB : GNATCOLL.SQL.Exec.Database_Connection;
-- Used to Query the data
--
Q : SQL_Query;
begin
-- Database Description
--
DB_Descr := GNATCOLL.SQL.Postgres.Setup ("mydb1", "parallels", "localhost", "MyPassword", 5432);
-- Database Connection
--
DB := DB_Descr.Build_Connection;
-- Query the data
--
Q := SQL_Select
(Fields => Person.first_name,
From => Person);
Free (DB); -- for all connections you have opened
Free (DB_Descr);
end Main;
When attempting to make a connection to the database, the process terminates successfully.
I'm unsure of the syntax that should be used for the Select statement. If anyone would be able to tell me how to perform a simple SELECT * FROM Person; statement from within GNAT CE 2019, it would be greatly appreciated.
Thank you,
Lloyd
Added 13/05/20
parallels#localhost gnatcoll_db2ada]$ ls
dborm.py gnatcoll-db2ada-main-generate.adb
dbschema.txt gnatcoll_postgres2ada.adb
gnatcoll_all2ada.adb gnatcoll_postgres2ada.gpr
gnatcoll_all2ada.gpr gnatcoll_sqlite2ada.adb
gnatcoll_db2ada.adb gnatcoll_sqlite2ada.gpr
gnatcoll-db2ada.ads Makefile
gnatcoll_db2ada.gpr makefile.setup
[parallels#localhost gnatcoll_db2ada]$ gnatcoll_postgres2ada -dbmodel dschema.txt/home/parallels/Desktop/dschema.txt
bash: gnatcoll_postgres2ada: command not found...
[parallels#localhost gnatcoll_db2ada]$
Added 15/05/20
prbuild -d -P/home/parallels/Documents/Ada Projects/TEST/default.gpr -XGNATCOLL_OS=unix -XBUILD=PROD -XGNATCOLL_HASPQPREPARE=yes -XGPR_BUILD=static -XLIBRARY_TYPE=static -XXMLADA_BUILD=static -XGNATCOLL_CORE_BUILD=static -XGNATCOLL_BUILD=static /home/parallels/Documents/Ada Projects/TEST/src/main.adb
Compile
[Ada] main.adb
Bind
[gprbind] main.bexch
[Ada] main.ali
Link
[link] main.adb
/home/parallels/opt/GNAT/2019/bin/../libexec/gcc/x86_64-pc-linux-gnu/8.3.1/ld: cannot find -lpq
collect2: error: ld returned 1 exit status
gprbuild: link of main.adb failed
gprbuild: failed command was: /home/parallels/opt/GNAT/2019/bin/gcc main.o b__main.o /home/parallels/Documents/Ada Projects/TEST/obj/database_names.o /home/parallels/Documents/Ada Projects/TEST/obj/database.o /home/parallels/gnatcoll-db/postgres/lib/static/libgnatcoll_postgres.a /home/parallels/gnatcoll-db/sql/lib/static/libgnatcoll_sql.a /home/parallels/opt/GNAT/2019/lib/gnatcoll.static/libgnatcoll.a /home/parallels/opt/GNAT/2019/lib/gpr/static/gpr/libgpr.a /home/parallels/opt/GNAT/2019/lib/xmla
da/xmlada_schema.static/libxmlada_schema.a /home/parallels/opt/GNAT/2019/lib/xmlada/xmlada_dom.static/libxmlada_dom.a /home/parallels/opt/GNAT/2019/lib/xmlada/xmlada_sax.static/libxmlada_sax.a /home/parallels/opt/GNAT/2019/lib/xmlada/xmlada_input.static/libxmlada_input_sources.a /home/parallels/opt/GNAT/2019/lib/xmlada/xmlada_unicode.static/libxmlada_unicode.a -lpq -L/home/parallels/Documents/Ada Projects/TEST/obj/ -L/home/parallels/Documents/Ada Projects/TEST/obj/ -L/home/parallels/gnatcoll-db/p
ostgres/lib/static/ -L/home/parallels/opt/GNAT/2019/lib/gnatcoll.static/ -L/home/parallels/opt/GNAT/2019/lib/xmlada/xmlada_dom.static/ -L/home/parallels/opt/GNAT/2019/lib/xmlada/xmlada_sax.static/ -L/home/parallels/opt/GNAT/2019/lib/xmlada/xmlada_unicode.static/ -L/home/parallels/opt/GNAT/2019/lib/xmlada/xmlada_input.static/ -L/home/parallels/opt/GNAT/2019/lib/xmlada/xmlada_schema.static/ -L/home/parallels/opt/GNAT/2019/lib/gpr/static/gpr/ -L/home/parallels/gnatcoll-db/sql/lib/static/ -L/home/par
allels/opt/GNAT/2019/lib/gcc/x86_64-pc-linux-gnu/8.3.1/adalib/ -static-libgcc /home/parallels/opt/GNAT/2019/lib/gcc/x86_64-pc-linux-gnu/8.3.1/adalib/libgnarl.a /home/parallels/opt/GNAT/2019/lib/gcc/x86_64-pc-linux-gnu/8.3.1/adalib/libgnat.a -lrt -lpthread -ldl -Wl,-rpath-link,/home/parallels/opt/GNAT/2019/lib/gcc/x86_64-pc-linux-gnu/8.3.1//adalib -Wl,-z,origin,-rpath,$ORIGIN/:$ORIGIN/../../../..//gnatcoll-db/postgres/lib/static:$ORIGIN/../../../..//opt/GNAT/2019/lib/gnatcoll.static:$ORIGIN/../../
../..//opt/GNAT/2019/lib/xmlada/xmlada_dom.static:$ORIGIN/../../../..//opt/GNAT/2019/lib/xmlada/xmlada_sax.static:$ORIGIN/../../../..//opt/GNAT/2019/lib/xmlada/xmlada_unicode.static:$ORIGIN/../../../..//opt/GNAT/2019/lib/xmlada/xmlada_input.static:$ORIGIN/../../../..//opt/GNAT/2019/lib/xmlada/xmlada_schema.static:$ORIGIN/../../../..//opt/GNAT/2019/lib/gpr/static/gpr:$ORIGIN/../../../..//gnatcoll-db/sql/lib/static:$ORIGIN/../../../..//opt/GNAT/2019/lib/gcc/x86_64-pc-linux-gnu/8.3.1/adalib -o main
[2020-05-15 14:56:50] process exited with status 4, 100% (30/30), elapsed time: 02.34s
Added 17/05/20
[SQL.ERROR] FATAL: Ident authentication failed for user "postgres"
_SQL.ERROR_ FATAL: Ident authentication failed for user "postgres"
_SQL.ERROR_ params="dbname='mydb1' user='postgres' host='localhost' sslmode=allow" ()
[SQL.ERROR] Failed to execute SELECT persons.person_uid, persons.first_name, persons.last_name, persons.gender, persons.email, persons.date_of_birth, persons.country_of_birth FROM persons error=No connection to database
FAILED
[2020-05-17 19:30:04] process terminated successfully, elapsed time: 00.19s
Added 29/05/20
home/parallels/Documents/Ada Projects/Connect to a DB/obj/main
[SQL.ERROR] select failed: SELECT persons.person_uid, persons.first_name, persons.last_name, persons.gender, persons.email, persons.date_of_birth, persons.country_of_birth FROM persons PGRES_FATAL_ERROR ERROR: relation "persons" does not exist
_SQL.ERROR_ LINE 1: ...persons.date_of_birth, persons.country_of_birth FROM persons
_SQL.ERROR_ ^
FAILED
[2020-05-29 22:40:11] process terminated successfully, elapsed time: 00.19s
postgres=# select * from persons;
person_uid | first_name | last_name | gender | email | date_of_birth | country_of_birth
--------------------------------------+------------+------------+--------+------------------------------+---------------+------------------
afbf64be-e7d5-45a1-b8fb-1a9fd66e2765 | Audrie | Vasyukov | Female | avasyukovd6#domainmarket.com | 1988-11-24 | Guatemala
ffda7264-1e54-428b-ae68-9ddb7b97702a | Nefen | Philippard | Male | nphilippardd7#economist.com | 2006-11-08 | Russia
169d5fb9-8d40-451e-8b02-cd1c3639fbed | Leonore | Garthland | Female | lgarthlandd8#furl.net | 1991-03-23 | Canada
e34f4f21-524c-4134-81d6-7fd1fd9a7537 | Yank | Turfitt | Male | yturfittd9#exblog.jp | 1990-02-07 | China
57336d0e-34f2-4166-a100-7b468e96a521 | Benn | Pawley | Male | bpawleyda#indiegogo.com | 2006-10-28 | Russia
b54a8411-3674-4432-b896-aaf35a10919b | Tod | Easen | Male | teasend4#php.net | 1990-08-24 | China
(6 rows)

Answer 1

The user manual states that you must first generate Ada data types that represent the entities (tables, fields, etc.) of the database with which you interact in order to use functions like SQL_Select. This can be done using the gnatcoll_db2ada utility (see here); either by some sort of reflection on the database or by providing a hand written schema (example in the user manual). Here are my own steps for creating an example.
Install dependencies:
$ sudo apt-get install postgresql libpq-dev
Create a database user (here: deedee):
$ sudo -u postgres bash
postgres#debian: $ createuser --pwprompt deedee
Clone gnatcoll-db:
$ git clone https://github.com/AdaCore/gnatcoll-db.git
Build and install gnatcoll-sql:
gnatcoll-db/sql $ make setup
gnatcoll-db/sql $ make
gnatcoll-db/sql $ sudo bash -c "PATH=$PATH:/opt/GNAT/2019/bin make install"
Build and install gnatcoll-postgress:
gnatcoll-db/postgress $ make setup
gnatcoll-db/postgress $ make
gnatcoll-db/postgress $ sudo bash -c "PATH=$PATH:/opt/GNAT/2019/bin make install"
Build and install gnatcoll_db2ada:
gnatcoll-db/gnatcoll_db2ada $ make setup DB_BACKEND=postgres
gnatcoll-db/gnatcoll_db2ada $ make
gnatcoll-db/gnatcoll_db2ada $ sudo bash -c "PATH=$PATH:/opt/GNAT/2019/bin make install"
The utility will be installed next to all other GNAT programs:
$ which gnatcoll_postgres2ada
/opt/GNAT/2019/bin/gnatcoll_postgres2ada
To use the utility, I first created a small database using the data you provided. I recreated the table persons using the commands:
$ sudo -u postgres bash
postgres#debian: $ createdb mydb1
postgres#debian: $ psql mydb1 < persons.sql
with
persons.sql
CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
CREATE TYPE gender AS ENUM ('Male', 'Female');
CREATE TABLE persons (
person_uid uuid DEFAULT uuid_generate_v4 () PRIMARY KEY,
first_name VARCHAR (20) NOT NULL,
last_name VARCHAR (20) NOT NULL,
gender gender NOT NULL,
email VARCHAR (50) NOT NULL,
date_of_birth DATE NOT NULL,
country_of_birth VARCHAR (20) NOT NULL
);
INSERT INTO persons (
first_name,
last_name,
gender,
email,
date_of_birth,
country_of_birth
)
VALUES
('Audrie' , 'Vasyukov' , 'Female', 'avasyukovd6#domainmarket.com', '1988-11-24', 'Guatemala'),
('Nefen' , 'Philippard', 'Male' , 'nphilippardd7#economist.com' , '2006-11-08', 'Russia' ),
('Leonore', 'Garthland' , 'Female', 'lgarthlandd8#furl.net' , '1991-03-23', 'Canada' ),
('Yank' , 'Turfitt' , 'Male' , 'yturfittd9#exblog.jp' , '1990-02-07', 'China' ),
('Benn' , 'Pawley' , 'Male' , 'bpawleyda#indiegogo.com' , '2006-10-28', 'Russia' ),
('Tod' , 'Easen' , 'Male' , 'teasend4#php.net' , '1990-08-24', 'China' );
GRANT SELECT ON persons TO deedee;
I then created a database schema (see user manual) and generated the Ada code:
$ gnatcoll_postgres2ada -dbmodel dschema.txt
$ ls
database.adb database.ads database_names.ads dschema.txt
with
dschema.txt
| TABLE | persons | || The contents of person |
| person_uid | TEXT | PK || Auto-generated id |
| first_name | TEXT | NOT NULL || First name |
| last_name | TEXT | NOT NULL || Last name |
| gender | TEXT | NOT NULL || Gender |
| email | TEXT | NOT NULL || E-mail address |
| date_of_birth | DATE | NOT NULL || Date of birth |
| country_of_birth | TEXT | NOT NULL || Country of birth |
I finally added a trace configuration file (based on the example in the GNATcoll user manual), adapted your example code and made it work with my own table:
.gnatdebug (write trace info to standard error; indicated by >&2)
>&2
SQL.yes
SQL.SELECT=yes
SQL.LITE=yes
default.gpr
with "gnatcoll_postgres.gpr";
project Default is
for Source_Dirs use ("src");
for Object_Dir use "obj";
for Main use ("main.adb");
end Default;
main.adb
with Ada.Text_IO; use Ada.Text_IO;
with GNATCOLL.Traces; use GNATCOLL.Traces;
with GNATCOLL.SQL.Postgres; use GNATCOLL.SQL.Postgres;
with GNATCOLL.SQL.Exec; use GNATCOLL.SQL.Exec;
with GNATCOLL.VFS; use GNATCOLL.VFS;
with GNATCOLL.SQL.Inspect; use GNATCOLL.SQL.Inspect;
with GNATCOLL.SQL; use GNATCOLL.SQL;
with Database;
procedure Main is
-- Datebase Description
DB_Descr : GNATCOLL.SQL.Exec.Database_Description;
-- Database Connection
DB : GNATCOLL.SQL.Exec.Database_Connection;
-- Used to Query the data
Q : SQL_Query;
begin
-- Enable tracing, so we can see if something goes wrong.
GNATCOLL.Traces.Parse_Config_File (".gnatdebug");
-- Database description.
DB_Descr := GNATCOLL.SQL.Postgres.Setup
(Database => "mydb1",
User => "deedee",
Host => "localhost",
Password => "xxxx");
-- Database connection.
DB := DB_Descr.Build_Connection;
-- Define the query.
Q := SQL_Select
(Fields =>
Database.Persons.Person_Uid & -- 0
Database.Persons.First_Name & -- 1
Database.Persons.Last_Name & -- 2
Database.Persons.Gender & -- 3
Database.Persons.Email & -- 4
Database.Persons.Date_Of_Birth & -- 5
Database.Persons.Country_Of_Birth, -- 6
From => Database.Persons);
declare
R : Forward_Cursor;
begin
-- Perform the actual query, show results if OK.
R.Fetch (DB, Q);
if Success (DB) then
while Has_Row (R) loop
Put_Line ("UUID . . : " & Value (R, 0));
Put_Line ("Name . . : " & Value (R, 1) & " " & Value (R, 2));
Put_Line ("Gender . : " & Value (R, 3));
Put_Line ("E-Mail . : " & Value (R, 4));
Put_Line ("Birth. . : " & Value (R, 5) & ", " & Value (R, 6));
New_Line;
Next (R);
end loop;
else
Put_Line ("FAILED");
end if;
end;
Free (DB); -- for all connections you have opened
Free (DB_Descr);
GNATCOLL.Traces.Finalize;
end Main;
build & output
$ gprbuild -P default.gpr
[...]
$ ./obj/main
[SQL.SELECT] SELECT persons.person_uid, persons.first_name, persons.last_name, persons.gender, persons.email, persons.date_of_birth, persons.country_of_birth FROM persons (6 tuples) PGRES_TUPLES_OK
UUID . . : 564b6d18-5f99-4d6b-8098-d5ce79910107
Name . . : Audrie Vasyukov
Gender . : Female
E-Mail . : avasyukovd6#domainmarket.com
Birth. . : 1988-11-24, Guatemala
UUID . . : a4c2743a-40ad-409e-9af7-f21e7b91da05
Name . . : Nefen Philippard
Gender . : Male
E-Mail . : nphilippardd7#economist.com
Birth. . : 2006-11-08, Russia
UUID . . : 04aa6123-b317-4be3-a1af-8a01d43ee60f
Name . . : Leonore Garthland
Gender . : Female
E-Mail . : lgarthlandd8#furl.net
Birth. . : 1991-03-23, Canada
UUID . . : e43ec5ef-3cd2-4d3c-8f3e-106b7c2f2ccf
Name . . : Yank Turfitt
Gender . : Male
E-Mail . : yturfittd9#exblog.jp
Birth. . : 1990-02-07, China
UUID . . : 3e1d6431-62d5-4d4b-8333-a92a66575f9f
Name . . : Benn Pawley
Gender . : Male
E-Mail . : bpawleyda#indiegogo.com
Birth. . : 2006-10-28, Russia
UUID . . : ae60db02-298a-43d3-81a2-59fcf610c045
Name . . : Tod Easen
Gender . : Male
E-Mail . : teasend4#php.net
Birth. . : 1990-08-24, China
APPENDIX
I used the default (non-customized) host-based authentication (hba) file.
pg_hba.conf
# Database administrative login by Unix domain socket
local all postgres peer
# TYPE DATABASE USER ADDRESS METHOD
# "local" is for Unix domain socket connections only
local all all peer
# IPv4 local connections:
host all all 127.0.0.1/32 md5
# IPv6 local connections:
host all all ::1/128 md5
# Allow replication connections from localhost, by a user with the
# replication privilege.
local replication all peer
host replication all 127.0.0.1/32 md5
host replication all ::1/128 md5