river jdbc 更新问题

{{{
PUT /_river/my_jdbc_river/_meta
{
"type" : "jdbc",
"strategy" : "simple",
"interval" : "6000",
"schedule" : "0 0-59 0-23 ? * *",
"flush_interval" : "5s",
"jdbc" : [ {
"url" : "jdbc:mysql://localhost:3306/test",
"user" : "root",
"password" : "",
"sql" : "select *, id as _id from test",
"index" : "dbs",
"type" : "table",
"versioning" : true,
"digesting" : false,
"autocommit" : true
}, {
"url" : "jdbc:mysql://localhost:3306/test",
"user" : "root",
"password" : "",
"sql" : "select *, id as _id from test",
"index" : "dbs",
"type" : "table",
"versioning" : true,
"digesting" : false,
"autocommit" : true
} ]
}
}}}

我这样建立一个 river，之后我再向里面加入自定义的 field，然后这个 river 自动更新以后，会把我加的自定义 field 删掉，看起来river 的更新机制就是先 delete，create，导致自定义的字段就没了

贴贴 代码呢