Modify an element of an array in MongoDB

2013年12月12日 · Miguel Parramón · blogger

Tags: dev diary, MongoDB

Let’s say you have a document in MongoDB like so:

{ “apple_pie” : { “ingredients” : [ “flour”, “orange”, “butter”, “sugar” ] } }

And you see that you’ve made a mistake there: one of the elements of the ingredients array should be changed, to apple. But how?

Turns out there’s an operator called ”$”, which, in an update operation, identifies an element in an array, without having to know its positional value. We would use it in this case like so:

db.recipes.update( {“apple_pie.ingredients”: “orange”}, { “$set”: {“apple_pie.ingredients.$”: “apple”} } )

Once we have selected an element on the query side of the update, we can refer to it with $. So, this update operation means: “select the array element named orange, and set it to apple”. 

You can find more info about this operator on the mongoDB docs, but I hope this post helps you find your way if you google for this problem :-)

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