Check if value exists in firebase DB
JavascriptFirebaseFirebase Realtime-DatabaseJavascript Problem Overview
Is there a method in firebase, which can check if value exist in DB? Firebase has method .exists(), but according to docs it checks only the keys.
I have the following structure:
{
"users": {
"-KKUmYgLYREWCnWeHCvO": {
"fName": "Peter",
"ID": "U1EL9SSUQ",
"username": "peter01"
},
"-KKUmYgLYREWCnWeHCvO": {
"fName": "John",
"ID": "U1EL5623",
"username": "john.doe"
}
}
}
I want to check if ID with value U1EL5623
exists.
Javascript Solutions
Solution 1 - Javascript
The exists()
method is part of the snapshot
object which is returned by firebase queries. So keep in mind that you won't be able to avoid retrieving the data to verify if it exists or not.
ref.child("users").orderByChild("ID").equalTo("U1EL5623").once("value",snapshot => {
if (snapshot.exists()){
const userData = snapshot.val();
console.log("exists!", userData);
}
});
Observations:
In case you are in a different scenario which you have the exact ref path where the object might be, you wont need to add orderByChild
and equalTo
. In this case, you can fetch the path to the object directly so it wont need any search processing from firebase. Also, if you know one of the properties the object must have you can do as the snippet below and make it retrieve just this property and not the entire object. The result will be a much faster check.
//every user must have an email
firebase.database().ref(`users/${userId}/email`).once("value", snapshot => {
if (snapshot.exists()){
console.log("exists!");
const email = snapshot.val();
}
});
Solution 2 - Javascript
This is a similar solution if you want to check if an email exists in firebase
firebase.app().database().ref("shops").orderByChild("email")
.equalTo(user.email).once("value", snapshot => {
const userData = snapshot.val();
// Check if it is a SHOP.
if (userData) {
console.log("Shop logged in!");
this.setState({
isAdminLoggedIn: false,
isUserLoggedIn: false,
isShopLoggedIn: true,
isNoneLoggedIn: false
});
// Check if it is a USER.
} else {
console.log("User logged in");
this.setState({
isAdminLoggedIn: false,
isUserLoggedIn: true,
isShopLoggedIn: false,
isNoneLoggedIn: false
});
}
});
Solution 3 - Javascript
I can't make comments yet, so I'm posting an answer:
To add to the suggested answer, if you wanted to query whether or not any users exist, you can try to improve performance by adding .limitToFirst(1) or .limitToLast(1). This way you can limit your retrieved data to the minimum:
//Check if any users exist
firebase.database().ref(`users`).limitToFirst(1).once("value", snapshot => {
if (snapshot.exists()){
console.log("exists!");
// TODO: Handle that users do exist
return true;
}
// TODO: Handle that users do not exist
});
sources: https://firebase.google.com/docs/reference/js/firebase.database.Query#limitToFirst
Solution 4 - Javascript
This is how I searched for a url value in Firebasebase database on my project:
const searchFirebase = (url, idx) =>
{
firebase
.app()
.database()
.ref("recipes")
.orderByChild("url")
.equalTo(url)
.once("value", (snapshot) => {
if (snapshot.exists()) {
const userData = snapshot.val();
console.log("exists!", userData);
document.querySelector(`[data-recipe-id="${idx}"]`)
.classList.replace('fav-heart', 'unfav-heart');
} else {
return false;
}
});
}