How to extract a particular field from a collection.findOne query result?

help
1

Hi
I am trying to extract a particular field from a result of a query

var categoryId = this.props.expensetype.categoryId;
console.log(categoryId); 
var categoryName = Categories.findOne({ _id : categoryId }, {name : 1, slNo : 0, _id : 0});
console.log(categoryName);

I see correct response in the first console message as

"mAprneqZkcgcZrqsv"

The second console log message returns the entire document from the collection Categories.

{_id: "mAprneqZkcgcZrqsv", slNo: 3, name: "Restaurants"}

I just want to display the “name” field. I thought findOne will reply the corresponding document. How do I do it?

Thanks
Sudheer

2

Did you try categoryName.name?

3

Yes. It is “undefined”.

I also tried the “fields” specifier as mentioned in the API docs

var categoryName = Categories.find({ _id : categoryId }, {fields : {name : 1, slNo : 0, _id : 0}});

and it resulted in an error “TypeError: null is not an object (evaluating ‘prevComponentInstance._currentElement’)”

Sudheer

4

Did you publish the documents already? Looks like if your second console.log worked then you should be able to do categoryName.name.

5

Your findOne syntax is slightly off (it should look more like the find syntax you posted). Assuming you are subscribed and the documents are available, this will work as expected:

var categoryName = Categories.findOne({ _id : categoryId }, { fields: {name : 1, slNo : 0, _id : 0} } ).name;
6

@townmulti: Thanks for that tip. I realized my mistake. I was subscribing to the collection in my createContainer. I moved the subscription outside of the class definition and made sure that it was executed before the component was created, and it worked correctly.
@robfallows: I tried that and it gives error “You cannot currently mix including and excluding fields.” Also if you just do “{ fields: {name : 1, slNo : 0, _id : 0} }”, then that also give error saying that “You may not observe a cursor with {fields: {_id: 0}}”. But your rest of the syntax worked correctly.

Thanks guys for all the help. Appreciate it.

Sudheer

1 Like