TypeError: Cannot read property 'title' of undefined Nodejs Mysql 查询结果

Question

This error doesn't happen always, but it's been happening frequently and i couldn't find any solution for it. Any help would be appreciated.

PS: the table in the database has the 'title' column and there are data in there.

The Code:

 async function selectNotificationData(control_message_id){
const sql = await new Promise((res,rej)=>{
    let query = "SELECT title, body ,url_push, img_push, url_type, status,silent,channel FROM control_message WHERE id_control_message =?";
    con.query(query, [control_message_id],(err,row)=>{
        if(err) throw err;
        let n =row[0];
        let pf=null;
        try{
            pf =  setPerFlagOptmized(n.title,n.body);
            res({not_data:n,pf})
        }
        catch (err) {

            console.log("[Row : "+row[0]+"]");
            console.log("[n : "+n+"]");
            console.log("ERROR IN SELECTING NOT DATA OR SETTING THE FLAG : "+err);
        }


    })
}).catch((error)=>{
    console.log("ERROR IN SELECTING Notification DATA : "+error);
});

The Error:

app_1    | /usr/src/app/node_modules/mysql/lib/protocol/Parser.js:437
app_1    |       throw err; // Rethrow non-MySQL errors
app_1    |       ^
app_1    |
app_1    | TypeError: Cannot read property 'title' of undefined
app_1    |     at Query.con.query (/usr/src/app/v4/message/controllers/expandWorker.js:669:57)
app_1    |     at Query.<anonymous> (/usr/src/app/node_modules/mysql/lib/Connection.js:526:10)
app_1    |     at Query._callback (/usr/src/app/node_modules/mysql/lib/Connection.js:488:16)
app_1    |     at Query.Sequence.end 
(/usr/src/app/node_modules/mysql/lib/protocol/sequences/Sequence.js:83:24)
app_1    |     at Query._handleFinalResultPacket 
(/usr/src/app/node_modules/mysql/lib/protocol/sequences/Query.js:149:8)
app_1    |     at Query.EofPacket 
(/usr/src/app/node_modules/mysql/lib/protocol/sequences/Query.js:133:8)
app_1    |     at Protocol._parsePacket 
(/usr/src/app/node_modules/mysql/lib/protocol/Protocol.js:291:23)
app_1    |     at Parser._parsePacket 
(/usr/src/app/node_modules/mysql/lib/protocol/Parser.js:433:10)
app_1    |     at Parser.write (/usr/src/app/node_modules/mysql/lib/protocol/Parser.js:43:10)
app_1    |     at Protocol.write (/usr/src/app/node_modules/mysql/lib/protocol/Protocol.js:38:16)

I tried to log

[Row : undefined]
[n : undefined]

The setPerFlagOptmized function:

 function setPerFlagOptmized(title,body){
    var t = (title.includes("|*") || title.includes("*|") || title.includes("{{") || title.includes("}}"));
    var b = (body.includes("|*") || body.includes("*|") || body.includes("{{") || body.includes("}}"));
    return (t || b) ? 1:0;
}

Answer 1

This probably happens when no record is found for the given query. err in the callback will not be defined in this case, instead row is just an empty array.

Since you don't have a check for that and directly access row[0] , which yields undefined , the error is thrown for n.title . So you should add the following check:

if(err) throw err;

if (!row.length) {
   // handle error - throw or return here
}
// ..rest of the code