我试图使用PostgreSQL 9.2中添加的row_to_json()函数将查询结果映射到JSON.
我很难找到将连接行表示为嵌套对象(1:1关系)的最佳方法
以下是我try 过的(设置代码:表、示例数据，后跟查询):
-- some test tables to start out with:
create table role_duties (
id serial primary key,
name varchar
);
create table user_roles (
id serial primary key,
name varchar,
description varchar,
duty_id int, foreign key (duty_id) references role_duties(id)
);
create table users (
id serial primary key,
name varchar,
email varchar,
user_role_id int, foreign key (user_role_id) references user_roles(id)
);
DO $$
DECLARE duty_id int;
DECLARE role_id int;
begin
insert into role_duties (name) values ('Script Execution') returning id into duty_id;
insert into user_roles (name, description, duty_id) values ('admin', 'Administrative duties in the system', duty_id) returning id into role_id;
insert into users (name, email, user_role_id) values ('Dan', 'someemail@gmail.com', role_id);
END$$;
查询本身:
select row_to_json(row)
from (
select u.*, ROW(ur.*::user_roles, ROW(d.*::role_duties)) as user_role
from users u
inner join user_roles ur on ur.id = u.user_role_id
inner join role_duties d on d.id = ur.duty_id
) row;
我发现如果我使用ROW()，我可以将结果字段分离成一个子对象，但它似乎仅限于一个级别.我不能插入更多的AS XXX条语句，因为我认为我在本例中应该需要这样做.
我得到了列名，因为我将该表的结果转换为适当的记录类型，例如::user_roles.
以下是该查询返回的结果:
{
"id":1,
"name":"Dan",
"email":"someemail@gmail.com",
"user_role_id":1,
"user_role":{
"f1":{
"id":1,
"name":"admin",
"description":"Administrative duties in the system",
"duty_id":1
},
"f2":{
"f1":{
"id":1,
"name":"Script Execution"
}
}
}
}
我想做的是为连接生成JSON(1:1也可以)，这样我可以添加连接，并将它们表示为它们连接到的父对象的子对象，例如:
{
"id":1,
"name":"Dan",
"email":"someemail@gmail.com",
"user_role_id":1,
"user_role":{
"id":1,
"name":"admin",
"description":"Administrative duties in the system",
"duty_id":1
"duty":{
"id":1,
"name":"Script Execution"
}
}
}
}