Node.js在.then链中重复数据库请求

Question

I use a promise .then chain. In this chain I calculate some bounds, build the sql statement and send a request to the database. If the database request gives no result, I want to change something by calculating the bounds and do the same steps again. I want to repeat this until there is a database result.

This is my code:

.then(function(){
    return calcBound.calcBounds(req.body,0);
  })
  .then(function(options){
    return sqlStatementBuilder.sqlStatementBuilder(options);
  })
  .then(function(statement){
    return db_request.db_request(statement);
  })
  .then(function(dbResult){
    if(dbResult.length <= 0){ // if there are no results from the database
      console.log("There are no results for this filter options");
      var newDBResult;
      do{
        newDBResult = calcBound.calcBounds(req.body, addToOffset)              
                .then(function(options){
                  return sqlStatementBuilder.sqlStatementBuilder(options);
                })
                .then(function(statement){
                  return db_request.db_request(statement);
                })
      } while(dbResult.length <= 0);
      return newDBResult.sort(sortArray.compareRecordId);
    }else{
      return dbResult.sort(sortArray.compareRecordId);
    }
  })

The while loop is not a good idea her this will end up as "heap out of memory".

What would be a better solution to do this?

Answer 1

Create a function dummyRecursiveFunction with addToOffset as a parameter and call it until you get results in dbResult

function dummyRecursiveFunction(addToOffset) {
  someFunction()
  .then(function(){
    return calcBound.calcBounds(req.body, addToOffset);
  })
  .then(function(options){
    return sqlStatementBuilder.sqlStatementBuilder(options);
  })
  .then(function(statement){
    return db_request.db_request(statement);
  })
  .then(function(dbResult) {
    if(dbResult.length > 0) {
      return dbResult.sort(sortArray.compareRecordId);
    } else {
      // newOffset: Your recalculated offset value.
      dummyRecursiveFunction(newOffset);
    }
  });
}