动态SQL

字符串连接

字符串连接的语法为 #{参数}，请看下面的代码:

@SQL("select id, uid, content from message order by #{:1}")
public List<Message> getMessages(String orderBy);

• 当orderBy传入id时，sql被解析为：select id, uid, content from message order by id
• 当orderBy传入uid时，sql被解析为：select id, uid, content from message order by uid
• 当orderBy传入content时，sql被解析为：select id, uid, content from message order by content

if语句

if语句主要存在两种形式，[xxx]表示xxx不出现或出现一次：

1. 不包含#elseif，语法为 #if(表达式) 字符串 [ #else 字符串 ] #end
2. 包含#elseif，语法为 #if(表达式) 字符串 #elseif(表达式) 字符串 [ #else 字符串 ] #end，这里的#elseif可以多个

不包含#elseif

@SQL("select uid, name from user where #if(:1>0) uid=:1 #else uid=-1 #end")
public User getUser(int uid);

• 当uid传入10时，将执行：select uid, name from user where uid = 10
• 当uid传入0时，将执行：select uid, name from user where uid = -1

包含#elseif

@SQL("select uid, name from user where #if(:1>0) uid=:1 #elseif(:1=0) uid=1 #else uid=-1 #end")
public User getUser(int uid);

• 当uid传入10时，将执行：select uid, name from user where uid = 10
• 当uid传入0时，将执行：select uid, name from user where uid = 1
• 当uid传入-5时，将执行：select uid, name from user where uid = -1