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    <p>Sounds like you want to use the $elemMatch operator in conjunction with the '$' positional operator:</p> <p><a href="http://docs.mongodb.org/manual/reference/operator/elemMatch/" rel="nofollow">http://docs.mongodb.org/manual/reference/operator/elemMatch/</a> <a href="http://docs.mongodb.org/manual/reference/operator/positional/" rel="nofollow">http://docs.mongodb.org/manual/reference/operator/positional/</a></p> <p>Let's take your example. Let's say you want to find the element in the user's "ownedItems" list where the "company_id" is 3, and update that element's "item_amount" by 5. That can be done in a single update statement like so: </p> <pre><code>Users.update( { userId: _id, ownedItems : { $elemMatch : { company_id : 3 } } }, { $inc : { ownedItems.$.item_amount : 5 } } ) </code></pre> <p>The <strong>$elemMatch</strong> operator makes it explicit which of the elements of the list you're querying for. You can then use the <strong>$</strong> operator in the modifier clause to refer to that matched element and make changes to it.</p> <p>If the "ownedItems" list of the user does not have any entry matching { "company_id" : 3 } then the above update will not do anything. If that happens, you can do a second update with the <strong>$addToSet</strong> operator to add a new entry like so:</p> <pre><code>Users.update( { userId: _id }, { $addToSet : { ownedItems : { company_id : 3, item_amount : 5 } } } ) </code></pre> <p><a href="http://docs.mongodb.org/manual/reference/operator/addToSet/" rel="nofollow">http://docs.mongodb.org/manual/reference/operator/addToSet/</a></p>
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    1. POHow to update field in array, only if other field matches value in MongoDB
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    1. COthanks for that answer! But may be I miss out some things.. I see here a 2 problems for my example. First, I do not know if Users collection have `company_id` so what happens if there is no field in user doc. And second 'problem', may be I'm not familiar with **$** operator, but as I thought it is return the **first** match of the query's array, so in array, it can increment the value, for example, of company_id = 1, if it will be the first match for query (sorry for so silly questions :) )?
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    2. COGood point! In that case, you'll have to do 2 updates. You can check the result of the original update I mentioned, and if it doesn't actually change anything (because the query didn't match), then do another update that uses $addToSet to add a new entry to the ownedItems list. I'll update my answer with the details. I'm not sure I understand your second question. Is it a problem that it will increment the first match in the list? Do you expect multiple entries in the list to have the same company_id?
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