How do I query PostgreSQL within GNAT CE 2019

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