I want to add a value to an array that is inside another array. My document is like:
{categories:[{categoryName:"a category", items:[{itemName:"an item", arrayOfValues:[1]}]}]}
I would like to use $addToSet to arrayValues. To do so I am doing an update with a query
table.update({"categories.items.itemName" : "anItem"}, {$addToSet: "categories.$.items.$.arrayOfValues":"10"})
but I get an error: can't append to array using string field name [$]
What am I doing wrong? Is it possible to update with nested arrays?
Thanks
Arrays inside arrays is considered bad mongodb design right now (mainly because you can't manipulate them efficiently, using $addToSet and friends). And you took it one step further and created arrays inside arrays inside arrays!
I understand that schema-less nature of MongoDB can cause a feeling that you can throw documents of any structure into it and handle them later. Unfortunately, this is not the reality. You have to know what you're doing, what features and limitations are there. In this case, you can't use positional operator to push element to a nested array.
Related
I'm making a scheduling app, and storing all the scheduled things in firebase with arrays. When I try to schedule something with the same string value, it fails and doesn't add it to the array. I don't know if this is something in swift I can edit, or if it's a firebase setting.
If it's something in swift, here's the code updating the array:
doc.updateData([
"Instructor": FieldValue.arrayUnion(["\(scheduleinstructor)"])
])
If it's something in firebase, could someone please explain a way around this or a simple fix I overlooked?
According to the documentation on adding items to an array:
arrayUnion() adds elements to an array but only elements not already present
So the fact that the duplicate entry is not added is by design. If you want to allow that, you'll have to:
Read the document with the array from the databae.
Extract the array from the document into your application code.
Add the item to the array.
Write the entire modified array back to the database.
First question on stackoverflow :)
I'm going through the Ruby course on Codecademy and I'm stuck on something.
fruits = ["orange", "apple", "banana", "pear", "grapes"]
fruits.sort! {|first, second| second <=> first}
print fruits
I don't know how to phrase this question. On Codecademy the assignment was to set up the array to be displayed in reverse on the console. After some research, I was able to figure it out. I understand how it works and the order to put it in the code not why. I'm aware that "<=>" compares two objects, but how do the items within the array become objects when we don't declare them as such?
Secondly, what is the purpose of writing this code in this way when we could do fruits.sort.reverse?
First question: At various points in its operation the sort method has to compare pairs of objects to see what their relative ordering should be. It does the comparison by applying the block you pass to sort, i.e., {|first, second| second <=> first}. Not sure what you mean by "how do the items within the array become objects when we don't declare them as such?". All data in ruby is an object, so there's no declaration or conversion needed given that all variables are object references.
Second question: Yes, you could do fruits.sort.reverse, but that would require additional work after the sort to do the reverse operation. Also, reverse can't handle more complex sorting tasks, such as sorting people by multiple criteria such as gender & last name, or hair color, height, and weight. Writing your own comparator can handle quite complex orderings.
String literals can be used to create string objects in Ruby, there is no need to use the String class to create the object. The following two are equivalent:
"Hello, world!"
String.new("Hello, world!")
More information can be found here.
Secondly, what is the purpose of writing this code in this way when we could do fruits.sort.reverse?
Please contact Codecademy about this, but I suspect it's for learning more about how <=> works.
I'm using OpenRefine to pull in information on publisher policies using the Sherpa Romeo API (Sherpa Romeo is a site that aggregates publisher policies). I've got that.
Now I need to parse the returned JSON so that those with certain pieces of information remain. The results I'm interested in need to include the following:
'any_website',
'any_repository',
'institutional_repository',
'non_commercial_institutional_repository',
'non_commercial_repository'
These pieces on information all fall under an array called "permitted_oa". For some reason, I can't even work out how to just pull out that array. I've tried writing grel expressions such as
value.parseJson().items.permitted_oa
but it never reutrns anything.
I wish I could share the JSON but it's too big.
I can see a couple of issues here.
Firstly the Sherpa API response items is an array (i.e. a list of things). When you have an array in the JSON, you either have to select a particular item from the array, or you have to explicitly work through the list of things in the array (aka iterate across the array) in your GREL. If you've previously worked with arrays in GREL you'll be familiar with this, but if you haven't
value.parseJson().items[0] -> first item in the array
value.parseJson().items[1] -> second item in the array
value.parseJson().items[2] -> third item in the array etc. etc.
If you know there is only ever going to be a single item in the array then you can safely use value.parseJson().items[0]
However, if you don't know how many items will be in the array and you are interested in them all, you will have to iterate over the array using a GREL control such as "forEach":
forEach(value.parseJson().items, v, v)
is a way of iterating over the array - each time the GREL finds an item in the array, it will assign it to a variable "v" and then you can do a further operation on that value using "v" as you would usually use "value" (see https://docs.openrefine.org/manual/grel#foreache1-v-e2 for an example of using forEach on an array)
Another possibility is to use join on the array. This will join all the things in an array into a string.
value.parseJson().items.join("|")
It looks like the Sherpa JSON uses Arrays liberally so you may find more arrays you have to deal with to get to the values you want.
Secondly, in the JSON you pasted "oa_permitted" isn't directly in the "item" but in another array called "publisher_policy" - so you'll need to navigate that as well. So:
value.parseJson().items[0].publisher_policy[0].permitted_oa[0]
would get you the first permitted_oa object in the first publisher_policy in the first item in the items array. If you wanted to (for example) get a list of locations from the JSON you have pasted you could use:
value.parseJson().items[0].publisher_policy[0].permitted_oa[0].location.location.join("|")
Which will give you a pipe ("|") separated list of locations based on the assumption there is only a single item, single publisher_policy and singe permitted_oa - which is true in the case of the JSON you've supplied here (but might not always be true)
I am trying to append/remove items from an array inside of a Firestore Document but every time the entire array is replaced instead of the new value being appended. I have tried both of the following:
batch.setData(["favorites": [user.uid]], forDocument: bookRef, options: SetOptions.merge())
batch.updateData(["favorites": [user.uid]], forDocument: bookRef)
I know that instead of an array I can use an object/dictionary but that would mean storing additional data that is irrelevant (such as the key), all I need is the ID's stored inside the array. Is this something that is currently possible in Firestore?
Update elements in an array
If your document contains an array field, you can use arrayUnion() and arrayRemove() to add and remove elements. arrayUnion() adds elements to an array but only elements not already present. arrayRemove() removes all instances of each given element.
let washingtonRef = db.collection("cities").document("DC")
// Atomically add a new region to the "regions" array field.
washingtonRef.updateData([
"regions": FieldValue.arrayUnion(["greater_virginia"])
])
// Atomically remove a region from the "regions" array field.
washingtonRef.updateData([
"regions": FieldValue.arrayRemove(["east_coast"])
])
See documentation here
Actually, nowadays it is possible. With latest updates db.collection.updateData
method actually appends new item to array instead of replacing it.
Example usage can be found in Firebase documentation.
If you need to do it manually, you can use
FieldValue.arrayUnion([user.uid])
Nope. This isn't possible.
Arrays tend to be problematic in an environment like Cloud Firestore where many clients could theoretically append or remove elements from an array at the same time -- if instructions arrive in a slightly different order, you could end up with out-of-bounds errors, corrupted data, or just a really bad time. So you either need to use a dictionary (where you can specify individual keys) or replace the entire array.
I want to compare two arrays of objects.
but there is not suitable method found for that method since it doesnt accept objects other from String, Integer etc..
I already override Equals method on the objects of the array.
But how do i pass the array to the method?
Assert.assertArrayEquals(esperado.getListaEquiposTorneo(), resultado.getListaEquiposTorneo());
//esperado.getListaEquiposTorneo(), resultado.getListaEquiposTorneo()) list 1 and 2 of objects made by me
First, you should be able to just use assertEquals
Assert.assertEquals(esperado.getListaEquiposTorneo(),
resultado.getListaEquiposTorneo());
I prefer to use Hamcrest as it gives better error messages
assertThat(actualArray,
IsArrayContainingInOrder.arrayContaining(
expectedArray));
assertThat(resultado.getListaEquiposTorneo(),
IsArrayContainingInOrder.arrayContaining(
esperado.getListaEquiposTorneo()));
IsArrayContainingInOrder
See Tomasz Nurkiewicz answer:
ArrayUtils.isEquals() from Apache Commons does exactly that. It also handles multi-dimensional arrays.
you can use a simple AssertTrue on the result