Pass data fetched from one apex method to another in lwc

Question

I have two js methods in my js file.

One methods fetches a set of fields from an particular object, using an apex class method.

 @wire(getSObjectFieldNames , { sObjectName : 'Contact' })
sObjectFieldNames({ error, data }) {
    if (data) {
        this.sObjectFieldDetails  = data;
        for(let fieldLabel in data){
            this.mapOfFieldLabelsWithAPI.push({fieldName:fieldLabel, label:data[fieldLabel]});
            this.columns = this.mapOfFieldLabelsWithAPI;
        }
        this.error = undefined;
    } else if (error) {
        this.error = error;
        this.data  = undefined;
    }
}

The second method should pass the set of fields - fetched from the previous method as parameter to another apex class - method and should fetch a record list having those field details

 @track error;
@track sObjectList ;

@wire(setSObjectRecordList , { sObjectName : 'Contact',
                               sObjectFieldList :  this.columns})    
sObjectRecordList({error, data }) {
    console.log( "*********");
    if (data) {
        console.log("__________"+JSON.stringify(this.columns));
        this.sObjectList = data;
    } else if (error) {
        this.error = error;
    }
}

My problem here is that for the second method this.columns is coming as undefined, so the second method is throwing an error :

    **Cannot read property 'columns' of undefined**

Answer 1

Wires must be written to receive dynamic properties. The second wire should be called like:

@wire(setSObjectRecordList , { sObjectName : 'Contact',
                               sObjectFieldList :  "$columns"})    
...

A parameter given as "$name" maps to this.name automatically. You may need to set the columns property as tracked depending on just how you manage the property content across your entire LWC.

NB: if at all possible you should try to use the uiRecordApi and related object info features since these behave well in their sharing of cached information and the propagation of tracked updates across the entire Lightning page.