Angular - Promise within Foreach Loop

Question

Below code is problematic because it is not returning anything. How do I fix it?

public checkExistence(value: Item, tableName: string, schema: string): Promise<string>{
  var result = "";
  this.configData.forEach(element => {
    if(element.key.tableName === tableName && element.checkExist != null){
      let uiValue = value[element.key.columnName];
      let refTargets = element.checkExist.split("|");
      refTargets.forEach(target => {
        let targetTableColumn = target.split(',', 2);
        let table = targetTableColumn[0];
        let column = targetTableColumn[1];
         this.getRefData(schema,table,column).then((value: string[]) => {
          if (!(value.indexOf(uiValue) > -1)){
           result = result + table + "," + column + "|";
          }
        })
      });
    }
  });
}

the whole purpose of this function is to check the existence of value[element.key.columnName] in some column of some reference tables. There could be multiple reference tables to check (and hence refTargets.forEach).

Ultimately I want this function to return a string that represents the list of table/columns which do not contain this value.

Found this similar case but not sure how to apply it to mine. Angular chaining promises from foreach loop

Starting to learn Angular and Promise, and appreciate if you can help.

IF you think this function could have been written in a better way, please let me know. I will accept it if it works :)

Sandeep Gupta · Accepted Answer · 2018-07-10 02:58:11Z

2

Try this.

Explaination: Following code

Makes a Promise array where each Promise will resolve to table + "," + column + "|" string.
Does Promise.all() on created Promise array. This will resolve to array of table + "," + column + "|" strings.
Return a Promise which will resolve to a string resulted concatanation of array of table + "," + column + "|" strings in step 2.

Code:

public checkExistence(value: Item, tableName: string, schema: string): Promise<string>{
            // var result = "";
            let promises:Promise<string>[] = [];
            this.configData.forEach(element => {
                if(element.key.tableName === tableName && element.checkExist != null){
                    let uiValue = value[element.key.columnName];
                    let refTargets = element.checkExist.split("|");
                    refTargets.forEach(target => {
                        let targetTableColumn = target.split(',', 2);
                        let table = targetTableColumn[0];
                        let column = targetTableColumn[1];
                        let promise: Promise<string> = this.getRefData(schema,table,column).then((value: string[]) => {
                            if (!(value.indexOf(uiValue) > -1)){
                                return /*result = result + */ table + "," + column + "|";
                            }
                            return "";
                        });

                        promises.push(promise);
                    });
                }
            });
            return Promise.all(promises)
                .then((results:string[])=>{
                    return results.join();
                })
        }

edited Jul 10, 2018 at 2:58

answered Jul 9, 2018 at 15:33

Sandeep Gupta

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3 Comments

xzk Over a year ago

Thanks a lot. This code gives me error at promises.push(promise), it is complaining about promises 'not defined' at run time...

Sandeep Gupta Over a year ago

Forgot to initialize promises at the time of declaeration. Now it should work fine

Ajas Aju Over a year ago

Very helpfull after wasting long time on this same.thank you

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