使用 sql 在 postgres 上复制模式不起作用答案

【问题标题】：Copy schema on postgres with sql not working使用 sql 在 postgres 上复制模式不起作用
【发布时间】：2015-02-02 15:22:00
【问题描述】：

我在 postgres 上有多租户应用程序，为了创建帐户，我复制了一个模式“模板”并将其重命名为帐户数据。

我使用“sql”变量来复制模式“_template”。当我执行此操作时，一切正常，但没有替换具有 DEFAULT 属性的列。但是在pgAdmin中直接执行sql时工作正常。

示例： “id bigint NOT NULL DEFAULT nextval('_template.table_id_seq'::regclass)” 这个 _template.table_id_seq... 应该是 [schemaname].table_id_seq

String sql = new String(
"DO " +
"$do$ " +
"DECLARE " +
"   objeto text; " +
"   buffer text; " +
"   source_schema text; " +
"   dest_schema text; " +
"   default_ text; " +
"   column_ text; " +
"BEGIN " +
" " +
"   source_schema := '_template'; " +
"   dest_schema   := '" + schema + "'; " +
" " +
"EXECUTE 'CREATE SCHEMA ' || dest_schema ; " +
" " +
"   FOR objeto IN " +
"       SELECT sequence_name::text FROM information_schema.SEQUENCES WHERE sequence_schema = source_schema " +
"   LOOP " +
"EXECUTE 'CREATE SEQUENCE ' || dest_schema || '.' || objeto; " +
"   END LOOP; " +
" " +
" " +
"   FOR objeto IN " +
"       SELECT table_name::text FROM information_schema.TABLES WHERE table_schema = source_schema " +
"   LOOP         " +
"       buffer := dest_schema || '.' || objeto; " +
"       EXECUTE 'CREATE TABLE ' || buffer || ' (LIKE ' || source_schema || '.' || objeto || ' INCLUDING CONSTRAINTS INCLUDING INDEXES INCLUDING DEFAULTS)'; " +
"FOR column_, default_ IN " +
"           SELECT column_name::text, REPLACE( column_default::text, source_schema, dest_schema ) FROM " +
"               information_schema.COLUMNS WHERE table_schema = source_schema AND table_name = objeto AND column_default LIKE 'nextval(%' || source_schema || '%)' " +
"       LOOP " +
"EXECUTE 'ALTER TABLE ' || buffer || ' ALTER COLUMN ' || column_ || ' SET DEFAULT ' || default_; " +
"       END LOOP; " +
" " +
"   END LOOP; " +
"END " +
"$do$    " 
);

这里是一个 sql var 输出的例子

DO $do$ 
DECLARE     
    objeto text;    
    buffer text;    
    source_schema text;     
    dest_schema text;   
    default_ text;  
    column_ text; 
BEGIN  
    source_schema := '_template';   
    dest_schema   := 'schemacopied';  

    EXECUTE 'CREATE SCHEMA ' || dest_schema ;   

    FOR objeto IN       
        SELECT sequence_name::text FROM information_schema.SEQUENCES WHERE sequence_schema = source_schema 

    LOOP 
        EXECUTE 'CREATE SEQUENCE ' || dest_schema || '.' || objeto;     
    END LOOP;       

    FOR objeto IN       
        SELECT table_name::text FROM information_schema.TABLES WHERE table_schema = source_schema   
    LOOP                
        buffer := dest_schema || '.' || objeto;         
        EXECUTE 'CREATE TABLE ' || buffer || ' (LIKE ' || source_schema || '.' || objeto || ' INCLUDING CONSTRAINTS INCLUDING INDEXES INCLUDING DEFAULTS)'; 

        FOR column_, default_ IN            
            SELECT column_name::text, REPLACE( column_default::text, source_schema, dest_schema ) FROM 
            information_schema.COLUMNS WHERE table_schema = dest_schema AND table_name = objeto AND column_default LIKE 'nextval(%' || source_schema || '%)'        

        LOOP 
            EXECUTE 'ALTER TABLE ' || buffer || ' ALTER COLUMN ' || column_ || ' SET DEFAULT ' || default_;         
        END LOOP;   
    END LOOP; 
END $do$

【问题讨论】：

标签： sql postgresql multi-tenant

【解决方案1】：

information_schema.COLUMNS.column_default 中引用的nextval(...) 表达式是动态生成的，以根据当前的search_path 包含或排除架构名称。

如果序列的架构不在search path 中，则该架构作为序列名称的前缀出现，否则不显示。

因此这个子句的结果，真假：

column_default LIKE 'nextval(%' || source_schema || '%)'

真的取决于search_path，这可以解释为什么它在某些情况下有效（您在 pgAdmin 中的测试）而不是在其他情况下。

为了不依赖它，你可以在块的持续时间内强制search_path，如：

DO $$
BEGIN
  SET LOCAL search_path TO public;
  ...
  ...
END
$$ LANGUAGE plpgsql;

或者您可以将search_path 设置为源架构，在这种情况下，这些架构相关的default 子句可能根本不需要任何后处理。

【讨论】：