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POUsing MongoDB, how do I update a sub-document of a sub-array when element position is unknown?
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copied!<p>I'm trying to update a sub-document of a sub-array, but I can't count on the element's position in the array to always be the same, so how do I update it.</p> <p>For example, here's my document, I just want to push another tag object (key/val) onto the <code>tags</code> array of <code>real_pagenum</code>: 1 of the pdf with the <code>_id</code> of <code>ObjectId("50634e26dc7c22c64d00000a")</code></p> <pre><code>{ "_id" : ObjectId("503b83dfad79cc8d26000004"), "pdfs" : [ { "_id" : ObjectId("50634e26dc7c22c64d00000a"), "pages" : [ { "real_pagenum" : 1, "_id" : ObjectId("50634e74dc7c22c64d00002b"), "tags" : [ { "key" : "Item", "val" : "foo" }, { "key" : "Item", "val" : "bar" } ] }, { "real_pagenum" : 2, "_id" : ObjectId("50634e74dc7c22c64d00002b") } ], "title" : "PDF3", "version" : 3 } ], } </code></pre> <p>To reiterate, the goal is to first target the right pdf by <code>_id</code>, then the right page by <code>real_pagenum</code> and push into that pdf's page's <code>tags</code> array.</p> <p>I had tried: </p> <pre><code>db.projects.update({'pdfs.pdf_id':ObjectId("50634e25dc7c22c64d000007")}, {$push:{'pages.$.tags':{'key':'foo','val':'bar'}}},false,false); </code></pre> <p>but that doesn't get to the level I need. I've read that I can use a <a href="https://stackoverflow.com/questions/10341151/mongodb-update-deep-array">combination of the positional operator with actual element position</a>, but again, I can't guarantee or know the element's position.</p>

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