Typescript define type with function test

Question

I am trying to create types that allow me to only search for specific things.

Lets assume I have this model and data:

interface UserModel {
    _id: string;
    username: string;
    party: UserPartyModel;
}

interface UserPartyModel {
    invites: number;
    rsvps: number;
}

//Test Data
{
    _id: '123',
    username: 'testuser',
    party: {
        invites: 18,
        rsvps: 3
    }
}

Using mongodb, I can query the root properties:

db.users.findOne({_id: '123'});
db.users.findOne({username: 'testuser'});

So I created this type to catch errors for things not in my model:

export declare type MongoManagerFilter<T> = {
    [P in keyof T]?: T[P];
};

Mongodb also allows you to search inside an object such as this:

db.users.findOne({'party.invites': 18});

As you can see, now that I am using the previous type, MongoManagerFilter , I get an error that 'party.invites' does not exist in UserModel .

So what I would like to do is run a function like so:

function isDotStringRegExp(obj: Object, dotKey: string): boolean {
    let keyData = dotKey.split('.');
    let objData = obj;

    for (let i = 0; i < keyData.length; i++) {
        let key = keyData[i];
        if (objData.hasOwnProperty(key)) {
            objData = objData[key];
        
            if (i === keyData.length - 1) {
                return true;
            }
        }
        else {
            return false;
        }
    }
}

And then add another type to do this:

export declare type MongoManagerDotStringFilter<T> = {
    [key: string]: (isDotStringRegExp(T, key) ? any : never);
};

Unfortunately, it won't let me run the isDotStringRegExp function in this type.

How do I achieve this?

Answer 1

You cannot call a function with a type. So the function call isDotStringRegExp(T, key) is not possible since both T and key are types.

If you want type-safe access with dot-notation, take a look at this question: https://stackoverflow.com/a/68412497/10857778

Answer 2

If you are looking on how to do this with Mongo, look at my other thread, specifically the playground code.

Typescript Conditional Types Not Figuring Out Type