Firebase orderByChild equalTo在没有数据时挂起

Question

see jsfiddle: http://jsfiddle.net/237ur2tf/14/

coinref.orderByChild("uuid").equalTo("xx")...

Query works fine when there is a match in the database. When there is no match, neither the callback nor error function is called.

Am I doing something wrong?... What would be the way around this?.

Many thanks. Pat/

Answer 1

That is the expected behavior. The relevant snippet from your fiddle is slightly longer:

// Get by child uuid AND uuid exists
coinsRef.orderByChild("uuid")
        .equalTo("4D4B2118-0435-439C-BA7C-99B9BD0DA7F4")
        .on('child_added', function(snapshot) {

This code says that "when there is an (existing or new) child added to this query, call me with its snapshot". Since there is no child, the child_added event doesn't fire.

If you want to check if there is a value , you should use a value event:

// Get by child uuid AND uuid exists
coinsRef.orderByChild("uuid")
        .equalTo("4D4B2118-0435-439C-BA7C-99B9BD0DA7F4")
        .on('value', function(snapshot) {
    console.log("found Coin: 4D4B2118-0435-439C-BA7C-99B9BD0DA7F4");

If you want to do anything with the specific coin, you'll need to forEach() in the callback:

snapshot.forEach(function(child) {
    console.log("The coin has value: "+child.val());
})

Is there any reason why you can't store the coins by their uuid? It sounds like that is already a universally unique identifies; so if it is possible to store them with that key, the lookup would be a lot cheaper:

coinsRef.child("4D4B2118-0435-439C-BA7C-99B9BD0DA7F4")
        .on('value', function(snapshot) {
    console.log("The coin has value: "+snapshot.val());
})