Multple SQL queries in Node with oracledb - node.js

Question

I'm new to Node and am having problems reading from Oracle.
I have the basic examples all set up and can issue basic queries, and process the results etc..
The problem I'm having is that I need to;
Execute one query (Q1)
For each item in the results of Q1 I need to execute a second query (Q2)
I need to combine the results of Q1 and Q2s into an array to return as a promise
I am struggling to find an example where I can perform #2 - call the same query multiple times for each item returned from Q1, using the same connection which was used for Q1.
My code is below - I first perform a read, then iterate through the results storing connection.execute objects which I then run via the Promise.all line - the result of which I just output as I want to get this working before I code the logic to combine the results of Q1 and Q2.
When I run this via mocha, the results of don't contain any data - I see the column headings but no data.
So what am I missing here?
// placeholder for the connection
let conn;
// return case list array
var caseList = [];
var queryList = [];
return new Promise((resolve, reject) => {
// retrieve connection
oracledb.getConnection({
user: dbconfig.user,
password: dbconfig.password,
connectString: dbconfig.connectString
}) // the connection is returned as a promise
.then(connection => {
console.log('Connected to the DB!');
// assign connection
conn = connection;
// execute statement
return connection.execute(
`select caseid, casereference, startdate from caseheader inner join orgobjectlink on caseheader.ownerorgobjectlinkid = orgobjectlink.orgobjectlinkid where orgobjectlink.username = :username`,
[params.username], {
outFormat: oracledb.OBJECT // set the output format to be object
}
);
})
.then(result => {
// iterate around rows
result.rows.forEach(row => {
var caseObj = {
caseID: row.CASEID,
reference: row.CASEREFERENCE,
dateAssigned: moment(row.STARTDATE).format('YYYY-MM-DD'),
username: params.username,
}
caseList.push(caseObj);
console.log(caseObj.caseID)
queryList.push(conn.execute(`select concernroleid, concernrolename from concernrole inner join caseparticipantrole on concernrole.concernroleid = caseparticipantrole.participantroleid where caseparticipantrole.caseid = :caseID and (caseparticipantrole.typecode = 'PRI' or caseparticipantrole.typecode = 'MEM')`,
[caseObj.caseID], {
outFormat: oracledb.OBJECT
}));
});
// build up queries
return Promise.all(queryList).then(results => {
console.log(results);
Promise.resolve(results);
}, err => {
console.log(err);
});
}).then({
if(conn){
console.log("Closing DB connection");
conn.close();
}
}).catch(err => {
console.log('Error', err);
});
});

Answer 1

Promise.all will not work for you as you want to use a single connection and as mentioned previously a connection will only do one thing at a time anyway. To solve this problem using promises, you'd have to build up and unwind a promise chain. I can show you an example, but it's nasty - probably better to just forget I mentioned it.
A better option would be to go into a simple for loop using async/await. I can show you can example of that too but again, I think this is the wrong move. We call this row by row fetching (a.k.a slow by slow).
It's likely the best solution for you will be to take the results from the first query and build up an array. Then execute the second query using one of these options to process the array. https://oracle.github.io/node-oracledb/doc/api.html#sqlwherein
You'll need to include the caseid column in the select clause and perhaps even order by that column so that post-processing of the result set is simplified in Node.js.
This solution has the potential to greatly improve performance and resource utilization, but that has to be balanced against the amount of data you have, the resources, etc. I could probably show you an example of this too, but it will take a bit longer and I'd want to get some more info from you to ensure we're on the right path.

Answer 2

One problem is the Promise.all().then... function doesn't return anything (and doesn't need the additional resolve()). The way to get this sorted is build small, testable, promise returning functions, and test them individually.
Starting simply, write a mocha test to connect to the database...
function connect() {
return oracledb.getConnection({
user: dbconfig.user,
password: dbconfig.password,
connectString: dbconfig.connectString
});
}
Here's one that can run a command on the db. Test this with a simple query that you know will return some results.
function executeCmd(connection, cmd, params) {
return connection.execute(cmd, params, { outFormat: oracledb.OBJECT });
}
With just these two (and one more) we can outline a simple function that does the job: connect to the database, run a select, process each result asynchronously, then disconnect.
function connectAndQuery(username) {
let connection;
return connect().then(result => {
connection = result;
let cmd = `select caseid, casereference, startdate from caseheader inner join orgobjectlink on caseheader.ownerorgobjectlinkid = orgobjectlink.orgobjectlinkid where orgobjectlink.username = :username`;
return executeCmd(connection, cmd, [username]);
}).then(result => {
let promises = result.rows.map(row => processCaseRow(connection, row, username));
return Promise.all(promises);
}).then(result => {
// result should be an array of caseObj's
return connection.close().then(() => result);
});
}
The last thing to build and test is a promise-returning function which processes a row from the main function above.
I had to take some liberty with this, but I think the objective is -- given a row representing a "case" -- build a case object, including a collection of "concernedRoles" that can be queried with the caseID. (that last bit was my idea, but you can build a separate collection if you like)
// return a promise that resolves to an object with the following properties...
// caseID, reference, dateAssigned, username, concernedRoles
// get concernedRoles by querying the db
function processCaseRow(connection, row, username) {
var caseObj = {
caseID: row.CASEID,
reference: row.CASEREFERENCE,
dateAssigned: moment(row.STARTDATE).format('YYYY-MM-DD'),
username: username
}
let cmd = `select concernroleid, concernrolename from concernrole inner join caseparticipantrole on concernrole.concernroleid = caseparticipantrole.participantroleid where caseparticipantrole.caseid = :caseID and (caseparticipantrole.typecode = 'PRI' or caseparticipantrole.typecode = 'MEM')`;
return executeCmd(connection, cmd, row.CASEID).then(result => {
caseObj.concernedRole = result
return caseObj
})
}