How to use the value of a property as the default value for another property?

Question

I have a mongoose schema and I would like to use the value of a property as default value for another property, something like:

schemaDef = { 
    myProperty: {type: String, required: true}
    ...
    otherProperty: {type: String, default: this.myProperty}
}

I thought it was possible but apparently is not, could someone confirm that and possibly give me a reference?

Answer 1

Though there's no built in way, you could write a few helper functions to behave it like you want. An example schema:

module.exports = function(){
    var schemaDef = {
        email : {type : String, required: true},
        secondaryEmail : {type : String, required: true, selfDefault: "email"},
        fullName : {type : String, required: true, selfDefault: {fields: ["firstName","middleName", "lastName"], space: true}},
        password: {type: String, required: true},
        firstName : {type : String, required: true},
        middleName : {type : String, required: true},
        lastName : {type : String, required: true}
    };
    var selfDefaults = initSelfDefaults(schemaDef);
    var UserSchema = new Schema(schemaDef);
    UserSchema.pre('validate', function(next) {
        setSelfDefaults(this, selfDefaults)
        next();
    });
    return mongoose.model("User", UserSchema);
};

You can place the following helper functions in other files to require and use them for all models/schemas:

// gets and returns all selfDefaults from the scehmaDef obj. Throws error if selfDefault reference is invalid
function initSelfDefaults(schemaDef){
    var defaults = {};
    for(var key in schemaDef){
        if(schemaDef[key].selfDefault){
            if(schemaDef[key].selfDefault.fields){
                schemaDef[key].selfDefault.fields.forEach(function(field){
                    if (!schemaDef[field]){
                        throw new Error(field + " is an invalid selfDefault reference")
                    }
                })
            }
            else if(!schemaDef[schemaDef[key].selfDefault]){
                throw new Error(schemaDef[key].selfDefault + " is an invalid selfDefault reference")
            }
            defaults[key] = schemaDef[key].selfDefault;
            delete schemaDef[key].selfDefault;
        }
    };
    return defaults
}

// sets the selfDefaults for the fields of the document being created if the fields are empty
function setSelfDefaults(doc, defaults){
    for(var key in defaults){
        if(!doc[key]){
            if(defaults[key].fields){
                var fields = [];
                for(var i=0; i<defaults[key].fields.length; i++){
                    if(doc[defaults[key].fields[i]]){
                        fields.push(doc[defaults[key].fields[i]])
                    }
                }
                doc[key] = defaults[key].space? fields.join(" ") : fields.join("");  
            }
            else{
                doc[key] = doc[defaults[key]];
            }
        }
    }
    return;
}

It doesn't work for nested schemas, but you can tweak the code to make it so.