hasMany在使用PostgreSQL的Grails中的怪异问题。 “错误：列 <column_name> 不存在”

Question

我在尝试使用PostgreSQL 9.1使“ hasMany”在Grails 2.0.1中工作时遇到了困难。 我有两张桌子：

CREATE TABLE "_QUESTIONS"
(
  "QUESTION_ID" bigint NOT NULL,
  "TEXT" text,
  CONSTRAINT "PK" PRIMARY KEY ("QUESTION_ID" )
)
WITH (
  OIDS=FALSE
);
ALTER TABLE "_QUESTIONS"
  OWNER TO postgres;

CREATE TABLE "_ANSWERS"
(
  "ANSWER_ID" bigint NOT NULL,
  "TEXT" text,
  "QUESTION_ID" bigint,
  CONSTRAINT "PK1" PRIMARY KEY ("ANSWER_ID" ),
  CONSTRAINT "FK" FOREIGN KEY ("QUESTION_ID")
      REFERENCES "_QUESTIONS" ("QUESTION_ID") MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
)
WITH (
  OIDS=FALSE
);
ALTER TABLE "_ANSWERS"
  OWNER TO postgres;

和两个域类：

class Question {
    String text

    String toString(){
        text
    }

    static constraints = {
    }    
    static hasMany = [answers: Answer]    
    static mapping = {
        table '`_QUESTIONS`'
        version false
        id generator: 'identity'
        id column: '`QUESTION_ID`'
        text column: '`TEXT`'
    }
}

class Answer {
    String text
    Question question

    String toString(){
        text
    }

    static constraints = {
    }

    static  belongsTo = [question : Question]

    static mapping = {
        table '`_ANSWERS`'
        version false
        id generator: 'identity'
        id column: '`ANSWER_ID`'
        text column: '`TEXT`'
        question column: '`QUESTION_ID`'
    }
}

我为它们都生成了视图和控制器，当我尝试浏览特定问题时，出现以下错误：

URI:/hasManyTest/question/show/1
Class:org.postgresql.util.PSQLException
Message:ERROR: column answers0_.question_id does not exist Position: 8

与堆栈跟踪：

Line | Method
->>    8 | runWorker in \grails-app\views\question\show.gsp
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

Caused by SQLGrammarException: could not initialize a collection: [hasmanytest.Question.answers#1]
->>   26 | doCall    in C__Users_root_IdeaProjects_hasManyTest_grails_app_views_question_show_gsp$_run_closure2
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
|     55 | run       in C__Users_root_IdeaProjects_hasManyTest_grails_app_views_question_show_gsp
|   1110 | runWorker in java.util.concurrent.ThreadPoolExecutor
|    603 | run       in java.util.concurrent.ThreadPoolExecutor$Worker
^    722 | run . . . in java.lang.Thread

Caused by PSQLException: ERROR: column answers0_.question_id does not exist
  Position: 8
->> 2103 | receiveErrorResponse in org.postgresql.core.v3.QueryExecutorImpl
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
|   1836 | processResults in     ''
|    257 | execute . in     ''
|    512 | execute   in org.postgresql.jdbc2.AbstractJdbc2Statement
|    388 | executeWithFlags in     ''
|    273 | executeQuery in     ''
|     96 | executeQuery in org.apache.commons.dbcp.DelegatingPreparedStatement
|     26 | doCall    in C__Users_root_IdeaProjects_hasManyTest_grails_app_views_question_show_gsp$_run_closure2
|     55 | run . . . in C__Users_root_IdeaProjects_hasManyTest_grails_app_views_question_show_gsp
|   1110 | runWorker in java.util.concurrent.ThreadPoolExecutor
|    603 | run . . . in java.util.concurrent.ThreadPoolExecutor$Worker
^    722 | run       in java.lang.Thread

在过去的几天里，我已经做了大量的体操运动，但似乎无济于事，当我删除关联时，一切都很好。 我是否缺少明显的东西？

Answer 1

问题似乎是Grails / GORM映射所做的假设与用于创建表的SQL之间的不匹配。

如果您在上述SQL中省略了表名和列名的引号，则表和列将不区分大小写。 来自http://wiki.postgresql.org/wiki/Things_to_find_out_about_when_moving_from_MySQL_to_PostgreSQL ：

PostgreSQL中的数据库，表，字段和列的名称是大小写无关的，除非您在它们的名称周围用双引号引起来，否则它们是区分大小写的。 在MySQL中，表名可以区分大小写，也可以不区分大小写，具体取决于您使用的操作系统。

如果使用以下方法创建表，则将Grails排除在方程之外：

CREATE TABLE "_QUESTIONS"
(
  "QUESTION_ID" bigint NOT NULL,
  "TEXT" text,
  CONSTRAINT "PK" PRIMARY KEY ("QUESTION_ID" )
)
WITH (
  OIDS=FALSE
);

然后：

test=> select * from _questions;
ERROR:  relation "_questions" does not exist
LINE 1: select * from _questions
                      ^
test=> select * from _QUESTIONS;
ERROR:  relation "_questions" does not exist
LINE 1: select * from _QUESTIONS;
                      ^
test=> select * from "_QUESTIONS";
 QUESTION_ID | TEXT 
-------------+------
(0 rows)

但是，如果创建的表没有表名和列名的引号，则：

CREATE TABLE _QUESTIONS
(
  QUESTION_ID bigint NOT NULL,
  TEXT text,
  CONSTRAINT PK PRIMARY KEY (QUESTION_ID)
)
WITH (
  OIDS=FALSE
);

然后：

test=> select * from _questions;
 question_id | text 
-------------+------
(0 rows)

test=> select * from _QUESTIONS;
 question_id | text 
-------------+------
(0 rows)

test=> select * from "_QUESTIONS";
ERROR:  relation "_QUESTIONS" does not exist
LINE 1: select * from "_QUESTIONS";
                  ^

Answer 2

我设法弄清楚了。 原来，为什么ORM尝试通过其小写名称访问关联列，更改名称解决了该问题。