How to get value of some field in firebase firestore android?

The Cloud Firestore client-side SDKs always read and returns full documents. There is no way to read a subset of the fields in a document.

You can retrieve the entire document, and then process the DocumentSnapshot to just use the fields you're interested. But this means you're using more bandwidth than needed. If this is a regular occurrence for your app, consider creating a secondary collection where each document contains just the fields you're interested in.

Also see Doug's answer here (for Swift): How to access a specific field from Cloud FireStore Firebase in Swift

Firebase allows a few ways to query like an RDBMS database. And these are very handy too. Try the Where clause. It returns a single document but u can add multiple filters. check for more

try this code:

//set a global variable
dataList: Array<any>;


const dataCollection = firebase.firestore().collection('data');
dataCollection.get(query => {
query.forEach(docs => {
this.dataList.push({id: doc.id, data:doc.data()});
  })
})