why in nginx lua "if not res" does not work when there is no record in mysql?

zzhihua114 · 2018-10-12T11:51:30+00:00

You can still use proxy_pass within content_by_lua, with a little indirection. That's what I was doing before I rewrote my code to use the lua-rest...

why in nginx lua "if not res" does not work when there is no record in mysql?

zzhihua114

here is my table in mysql:

my query code：

-- query
                local query_str = "select status from buystatus where uid='"..message["uid"].."'";
                ngx.log(ngx.NOTICE, "query string: ", query_str);
                local res, err, errno, sqlstate = db:query(query_str);
                if not res then
                        insert_str = "insert into buystatus values('"..message["uid"].."',"..message["status"]..")";
                        ngx.log(ngx.ERR, "insert string: ", insert_str);
                        db:query(insert_str);
                        local msg = {};
                        msg["code"]=200;
                        msg["msg"]="Insert a new record success.";
                        to_send=cjson.encode(msg);
                        ngx.say(to_send);
                        return
                end

                update_str = "update buystatus set status="..message["status"].." where uid='"..message["uid"].."'";
                db:query(update_str)

when I search a record uid is u888， then my code will execute UPDATE part rather than INSERT part.

zzhihua114

And I compare "#res" with zero instead to implement the same target.

在 2018年10月12日星期五 UTC+8上午11:51:30，zzhih...@gmail.com写道：

here is my table in mysql:

my query code：
-- query local query_str = "select status from buystatus where uid='"..message["uid"].."'"; ngx.log(ngx.NOTICE, "query string: ", query_str); local res, err, errno, sqlstate = db:query(query_str); if not res then insert_str = "insert into buystatus values('"..message["uid"].."',"..message["status"]..")"; ngx.log(ngx.ERR, "insert string: ", insert_str); db:query(insert_str); local msg = {}; msg["code"]=200; msg["msg"]="Insert a new record success."; to_send=cjson.encode(msg); ngx.say(to_send); return end update_str = "update buystatus set status="..message["status"].." where uid='"..message["uid"].."'"; db:query(update_str)

when I search a record uid is u888， then my code will execute UPDATE part rather than INSERT part.

bogdan

Log the value of "type(res)" to make sure you expect a null value or a string with 0 characters. I think the resulting variable "res", in case of error, is something in the lines of "ngx.null", but I'm not sure ("ngx.null" will have type "object"). This happens with Redis, because "ngx.null" can be a value in an array, whereas Lua's "nil" can't be.

zzhihua114@gmail.com wrote:

And I compare "#res" with zero instead to implement the same target.

在 2018年10月12日星期五 UTC+8上午11:51:30，zzhih...@gmail.com写道：

    here is my table in mysql:

    tmp.png

    my query code：
    ||
    ||
    --query
    localquery_str ="select st atus from buystatus where
    uid='"..message["uid"].."'";
                   ngx.log(ngx.NOTICE,"query string: ",query_str);
    localres,err,errno,sqlstate =db:query(query_str);
    ifnotres then
                           insert_str ="insert into buystatus
    values('"..message["uid"].."',"..message["status"]..")";
                           ngx.log(ngx.ERR,"insert string: ",insert_str);
                         &nb sp; db:query(insert_str);
    localmsg ={};
                           msg["code"]=200;
                           msg["msg"]="Insert a new record success.";
                           to_send=cjson.encode(msg);
                           ngx.say(to_send);
    return
    end

                  &nbs p; update_str ="update buystatus set
    status="..message["status"].." where uid='"..message["uid"].."'";
                   db:query(update_str)

    when I search a record uid is u888， then my code will execute
    UPDATE part rather than INSERT part..

zzhihua114

I found another blog says that using "next(res)==nil" rather "#res" to see if res is empty or not.

在 2018年10月12日星期五 UTC+8下午5:34:07，bogdan写道：

Log the value of "type(res)" to make sure you expect a null value or a string with 0 characters. I think the resulting variable "res", in case of error, is something in the lines of "ngx.null", but I'm not sure ("ngx.null" will have type "object"). This happens with Redis, because "ngx.null" can be a value in an array, whereas Lua's "nil" can't be.

zzhih...@gmail.com wrote:

And I compare "#res" with zero instead to implement the same target.

在 2018年10月12日星期五 UTC+8上午11:51:30，zzhih...@gmail.com写道：

    here is my table in mysql:

    tmp.png

    my query code：
    ||
    ||
    --query
    localquery_str ="select st atus from buystatus where
    uid='"..message["uid"].."'";
                   ngx.log(ngx.NOTICE,"query string: ",query_str);
    localres,err,errno,sqlstate =db:query(query_str);
    ifnotres then
                           insert_str ="insert into buystatus
    values('"..message["uid"].."',"..message["status"]..")";
                           ngx.log(ngx.ERR,"insert string: ",insert_str);
                         &nb sp; db:query(insert_str);
    localmsg ={};
                           msg["code"]=200;
                           msg["msg"]="Insert a new record success.";
                           to_send=cjson.encode(msg);
                           ngx.say(to_send);
    return
    end

                  &nbs p; update_str ="update buystatus set
    status="..message["status"].." where uid='"..message["uid"].."'";
                   db:query(update_str)

    when I search a record uid is u888， then my code will execute
    UPDATE part rather than INSERT part..