问题:

I have document like

{
    id : 100,
    heros:[
        {
           nickname : "test",
           spells : [
             {spell_id : 61, level : 1},
             {spell_id : 1, level : 2}
           ]
        }
    ]
}

I can't $set spell's level : 3 with spell_id : 1 inside spells that inside heros with nickname "test. I tried this query:

db.test.update({"heros.nickname":"test", "heros.spells.spell_id":1}, 
{$set:{"heros.spells.$.level":3}});

Errror i see is

can't append to array using string field name [spells] Thanks for help.

回答1:

You can only use the $ positional operator for single-level arrays. In your case, you have a nested array (heros is an array, and within that each hero has a spells array).

If you know the indexes of the arrays, you can use explicit indexes when doing an update, like:

> db.test.update({"heros.nickname":"test", "heros.spells.spell_id":1}, {$set:{"heros.0.spells.1.level":3}});

回答2:

Try something like this:

db.test.find({"heros.nickname":"test"}).forEach(function(x) {  
    bool match = false;
    for (i=0 ; i< x.heros[0].spells.length ; i++) {
        if (x.heros[0].spells[i].spell_id == 1) 
        {
            x.heros[0].spells[i].level = 3;
            match = true;
        }
    }
    if (match === true) db.test.update( { id: x.id }, x );
});

Apparently someone opened a ticket to add the ability to put a function inside the update clause, but it hasn't been addressed yet: https://jira.mongodb.org/browse/SERVER-458