swi序言mysql + web [英] swi prolog mysql + web

问题描述

对不起，我的英语. 我想创建一个简单的网站，该网站将从mysql数据库中获取数据并将其显示在页面上. 我有两个问题:

Sorry for my English. I want to create a simple website that will take data from the mysql database and display it on the page. I have two problems:

1)使用在单独的模块中建立的数据库:

1) work with a database made in separate modules:

% database.pl
:- module(database,
 [ create_db_connect/0,
 use_database/0,
 query_to_database/1,
 disconnect_database/0
 ]).

:- use_module(library(odbc)).

create_db_connect :-
 odbc_connect('test', _,
       [ user('root'),
         password('123')
         alias(myblog),
         open(once)
 ]).

use_database :-
 odbc_query(myblog, 'use test', _).

query_to_database(X):-
 odbc_query(myblog, 'SELECT data FROM testtable where id = 4', row(X)).

disconnect_database :- odbc_disconnect(myblog).

将此模块导入主文件:

% el.pl
:- use_module(library(http/thread_httpd)).
:- use_module(library(http/http_dispatch)).
:- use_module(library(http/html_write)).
:- use_module(library(http/http_parameters)).
:- use_module(library(http/html_head)).

:- use_module(database).

:- http_handler(root(.), home, []).

server(Port): -
 http_server(http_dispatch, [port(Port)]).


home(_Request): -
 reply_html_page (
 title('Sql'),
 [\ main_page
 ]).

main_page -->
 create_db_connect,
 use_database,
 query_to_database(X),
 disconnect_database,
 html(div('id="tab_c2"', p('~w')-[X])).

在这种情况下，出现错误:

In this case, get the error:

Warning: The predicates below are not defined. If these are defined
Warning: at runtime using assert / 1, use: - dynamic Name / Arity.
Warning:
Warning: create_db_connect/2, which is referenced by
Warning: /root/prologDev/el.pl:56:17: 1-st clause of main_page/2

但是为什么呢?我在模块database.pl中定义了它！

But why? I defined it in the module database.pl!

2)虽然我不喜欢这个决定，但是我对此进行了调整:database.pl模块:

2) Although I do not like the decision, but I adjusted the module database.pl on this:

:- module (database,
 [ create_db_connect/2,
   use_database/2,
   query_to_database/3,
   disconnect_database/2
 ]).

:- use_module(library(odbc)).

create_db_connect(_, _) :-
 odbc_connect('test', _,
 [ user('root'),
   password('123'),
   alias(myblog),
   open(once)
 ]).

use_database(_, _) :-
 odbc_query(myblog, 'use test', _).
query_to_database(X, _, _) :-
 odbc_query(myblog, 'SELECT data FROM testtable where id = 4', row(X)).
disconnect_database(_, _) :- odbc_disconnect(myblog).

现在，该页面为空. 当我停止swipl whit停止时，会发生错误: my_thread_global_end()中的错误:1个线程没有退出.

And now, the page is empty. When I stop swipl whit halt, an error occurs: Error in my_thread_global_end (): 1 threads did not exit.

我做错了什么?

推荐答案

请注意，main_page//0是非终结符，不是谓词.要从main_page//0调用数据库谓词，您需要编写如下内容:

Note that main_page//0 is a non-terminal, not a predicate. To call your database predicates from the main_page//0, you need to write something like:

main_page -->
   {create_db_connect,
   use_database,
   query_to_database(X),
   disconnect_database},
   html(div('id="tab_c2"', p('~w')-[X])).

{}/1构造允许您从(规则的)语法规则中调用谓词.没有它，create_db_connect和其他将被解释为对其他非终端(create_db_connect//0，...)的调用.

The {}/1 construct allows you to call predicates from (the body of) grammar rules. Without it, create_db_connect and the others would be interpreted as calls to other non-terminals (create_db_connect//0, ...).

通常，通过附加两个参数将非终结符扩展为谓词.因此，您会收到以下警告:

Typically, non-terminals are expanded into predicates by appending two arguments. Hence the warnings you got:

Warning: create_db_connect/2, which is referenced by
Warning: /root/prologDev/el.pl:56:17: 1-st clause of main_page/2

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