I have an XML file in the following link
I want to populate a map that with ids of movies and the average of their corresponding ratings. I am trying the following command from this site
for $doc in db:open("movies","movies.xml")/movies/movie
let $map:= map:map()
let $key := map:put($map, $doc/#id, avg($doc/ratings/child::node()))
return $map
However, it doesn't run. I get an exception, Expecting variable declaration. What am I doing wrong?
EDIT:
I am trying it the following command
let $map:=map{}
for $doc in db:open("movies","movies.xml")/movies/movie
return
map:put($map,
$doc/#id,avg($doc/ratings/child::node())
)
I get seperate maps
As outlined in my comment, the map syntax MarkLogic uses has nothing to do with the XQuery 3.1 term map. MarkLogic implemented this map structure before the official XQuery spec defined it (this structure is rather new). So you can use the map as documented in the MarkLogic docs only when you use MarkLogic, it is a proprietary extension.
On the other hand, BaseX supports the XQuery 3.1 construct map. Therefore you should follow what is documented at the BaseX documentation. And this makes it actually shorter and side-effect free. You could e.g. do:
map:merge(for $movie in db:open("movies","movies.xml")/movies/movie return map:entry($movie/#id, avg($movie/ratings/child::node())))
You could also use map:put, but it doesn't make much sense for this use case as you would create a new map each time you call the map:put() function.
Related
recently started learning Rust and I am having some problems with syntax.
Can anyone explain to me this line:
// Stores all the kitties, key is the kitty id / index
pub Kitties get(fn kitties): map hasher(blake2_128_concat) u32 => Option<Kitty>;
So we're creating here public Kitties(variable) that accepts some function.
Kitties is of a type map hasher(blake2_128_concat) u32 which returns Option
map hasher? Also couldn't find hasher in documentation.
Based on the link you posted in the comments, the code snippet is part of a larger snippet that looks something like
decl_storage! {
trait Store for Module<T: Trait> as SimpleMap {
SimpleMap get(fn simple_map): map hasher(blake2_128_concat) T::AccountId => u32;
}
}
The decl_storage! call is a macro (macro calls are always ended in an exclamation point, like vec! or println!), which in essence means it can do whatever it wants with the stuff that follows it. In particular, the things inside the outer braces needn't be valid Rust, as decl_storage! can transform the contents freely.
My guess (at a quick Google search) is that decl_storage! refers to this macro, so you'll have to refer to its documentation to see what it expects.
This is a macro rule. Not origin Rust syntax.
Check this out: https://substrate.dev/rustdocs/v3.0.0/frame_support/macro.decl_storage.html
If you want to learn more about Map storage type in substrate check this, it also explains what hasher is:
https://substrate.dev/recipes/storage-maps.html
This Question is in reference with Data Hub Framework-
I am having 3-4 conditions in which i am doing operations like xdmp:node-replace and xdmp:document-delete and after all the conditions i am trying to insert the document using xdmp:document-insert.
When i am running the conditions independently by commenting the other conditions then it is working fine but if i am trying to run 2 or more conditions together- i am getting XDMP-CONFLICTINGUPDATES
$envelope is coming from STAGING Database which i am using in writer.xqy
The code sample is as below-
let $con1 := if($envelope/*:test/text() eq "abc")
then xdmp:node-replace(....) else ()
let $con2 := if($envelope/*:test/text() eq "123")
then xdmp:node-replace(....) else ()
let $con1 := if($envelope/*:test/text() eq "cde")
then xdmp:document-delete(....) else ()
return if($envelope//*FLAG/text() eq "1")
then
xdmp:document-insert($id, $envelope, xdmp:default-permissions(), map:get($options, "entity"))
Any Suggestions ?
XDMP-ConflictingUpdates means you are trying to update the same node more than once within a single transaction. Solving these types of errors can be infamously tricky and are a rite of passage for every MarkLogician.
In your case, this is caused by updating a node with xdmp:node-replace and then updating the document node which is the parent of that node with xdmp:document-insert. Thus, because you are updating both the node and its parent, you are in effect updating that node twice causing the error. Or, this may also occur from trying to both delete and insert a document at the same URI within the same transaction.
Here is a simple query you can run in QConsole to reproduce this behavior:
xquery version "1.0-ml";
xdmp:document-insert("/test.xml", <test><value></value></test>);
xquery version "1.0-ml";
let $d := fn:doc("/test.xml")
let $_ := xdmp:node-replace($d//value, <value>test</value>)
return
xdmp:document-insert("/test.xml", $d)
In the case of this demonstration, as well as your code, the xdmp:document-insert is redundant and can simply be removed.
Likely the XQuery statement above is attempting multiple updates to the same node in the same single-statement transaction. The xdmp:node-replace calls are performing updates at each operation to the same node. See the documentation for more details.
Here are two solutions that may work for you
Use conditional statements to decide what kind of update needs to be performed on the node, e.g., whether the node need to be deleted, whether the node needs to be updated and how. At the end of your script you could then apply the update behavior to the node.
Perform in-memory updates to the node then commit the node to the database at the end of the transaction. Here is one library you could use https://github.com/ryanjdew/XQuery-XML-Memory-Operations
One general possibility for complicated updates: use XSLT.
This is multi transaction statement. There are multiple ways to handle it in your scenario:
Use xdmp:eval
Use mem library of MarkLogic to replace your nodes
Rewrite your Query to avoid transaction conflict
I am writing code that needs to return a modified version of an XML node, without changing the original node in the parent document.
How can I copy/clone the node so that the original context will not be connected to/affected by it? I don't want changes made to this node to change the original node in the parent document, just to the copy that my function is returning.
What I'm looking for would be very similar to whatever cts:highlight is doing internally:
Returns a copy of the node, replacing any text matching the query
with the specified expression. You can use this function to easily
highlight any text found in a query. Unlike fn:replace and other
XQuery string functions that match literal text, cts:highlight matches
every term that matches the search, including stemmed matches or
matches with different capitalization. [marklogic docs > cts:highlight]
The easiest way to create a clone/copy of a node is to use the computed document node constructor:
document{ $doc }
If you are cloning a node that is not a document-node(), and don't want a document-node(), just a clone of the original node(), then you can XPath to select that cloned node from the new document-node():
document{ $foo }/node()
Just for completeness: in general, the standard XQuery Update Facility has copy-modify expressions that explicitly perform a copy. With no modifications, this is like explicit cloning.
copy $node := $foo
modify ()
return $node
I am not sure if MarkLogic supports this syntax or not though. As far as I know, it uses its own function library for updates.
In-memory XML nodes are not directly modifiable. Instead, you make your desired changes while constructing a new node. If you know XSLT, that can be a good way to do it. If not, you can use an XQuery technique called recursive descent.
I would like to execute this kind of flwor query (I am using Saxon) :
for $baseItem in collection('file:/xmlDir?select=*.xml;recurse=yes')/item
let $itemToRetrieve := xs:string($baseItem/item)
let $itemFilter := xs:string($baseItem/filter)
let $fileName := tokenize("*xmlPath($baseItem)*"),'/')[last()]
where $itemFilter = 'test'
return ($itemToRetrieve, $fileName)
This way I could quickly find, when working on a large collection, where the returned items where found by the processor, without having to use a external program, like find commands.
I have tried to use document-uri() and base-uri() functions but without success.
Is there a way to achieve this ?
The document-uri() function should give you what you want. I just tried
collection($someURI)!document-uri(.)
and it works for me provided the items in the collection are all document nodes (but it fails with a type error if the collection includes non-XML resources which are retrieved as items other than document nodes)
Another approach is to use uri-collection() which gives you the URIs of the resources rather than the resources themselves; you can then fetch the particular resources you want using the doc() function (or json-doc() or unparsed-text() depending on the type of resource).
Can someone tell me the exact difference between node() and element() types in XQuery? The documentation states that element() is an element node, while node() is any node, so if I understand it correctly element() is a subset of node().
The thing is I have an XQuery function like this:
declare function local:myFunction($arg1 as element()) as element() {
let $value := data($arg1/subelement)
etc...
};
Now I want to call the function with a parameter which is obtained by another function, say functionX (which I have no control over):
let $parameter := someNamespace:functionX()
return local:myFunction($parameter)
The problem is, functionX returns an node() so it will not let me pass the $parameter directly. I tried changing the type of my function to take a node() instead of an element(), but then I can’t seem to read any data from it. $value is just empty.
Is there some way of either converting the node to an element or should am I just missing something?
EDIT: As far as I can tell the problem is in the part where I try to get the subelement using $arg1/subelement. Apparently you can do this if $arg1 is an element() but not if it is a node().
UPDATE: I have tested the example provided by Dimitre below, and it indeed works fine, both with Saxon and with eXist DB (which is what I am using as the XQuery engine). The problem actually occurs with the request:get-data() function from eXist DB. This function gets data provided by the POST request when using eXist through REST, parses it as XML and returns it as a node(). But for some reason when I pass the data to another function XQuery doesn’t acknowledge it as being a valid element(), even though it is. If I extract it manually (i.e. copy the output and paste it to my source code), assign it to a variable and pass it to my function all goes well. But if I pass it directly it gives me a runtime error (and indeed fails the instance of test).
I need to be able to either make it ignore this type-check or “typecast” the data to an element().
data() returning empty for an element just because the argument type is node() sounds like a bug to me. What XQuery processor are you using?
It sounds like you need to placate static type checking, which you can do using a treat as expression. I don't believe a dynamic test using instance of will suffice.
Try this:
let $parameter := someNamespace:functionX() treat as element()
return local:myFunction($parameter)
Quoting from the 4th edition of Michael Kay's magnum opus, "The treat as operator is essentially telling the system that you know what the runtime type is going to be, and you want any checking to be deferred until runtime, because you're confident that your code is correct." (p. 679)
UPDATE: I think the above is actually wrong, since treat as is just an assertion. It doesn't change the type annotation node(), which means it's also a wrong assertion and doesn't help you. Hmmm... What I really want is cast as, but that only works for atomic types. I guess I'm stumped. Maybe you should change XQuery engines. :-) I'll report back if I think of something else. Also, I'm curious to find out if Dimitre's solution works for you.
UPDATE #2: I had backpedaled here earlier. Can I backpedal again? ;-) Now my theory is that treat as will work based on the fact that node() is interpreted as a union of the various specific node type annotations, and not as a run-time type annotation itself (see the "Note" in the "Item types" section of the XQuery formal semantics.) At run time, the type annotation will be element(). Use treat as to guarantee to the type checker that this will be true. Now I wait on bated breath: does it work for you?
EXPLANATORY ADDENDUM: Assuming this works, here's why. node() is a union type. Actual items at run time are never annotated with node(). "An item type is either an atomic type, an element type, an attribute type, a document node type, a text node type, a comment node type, or a processing instruction type."1 Notice that node() is not in that list. Thus, your XQuery engine isn't complaining that an item has type node(); rather it's complaining that it doesn't know what the type is going to be (node() means it could end up being attribute(), element(), text(), comment(), processing-instruction(), or document-node()). Why does it have to know? Because you're telling it elsewhere that it's an element (in your function's signature). It's not enough to narrow it down to one of the above six possibilities. Static type checking means that you have to guarantee—at compile time—that the types will match up (element with element, in this case). treat as is used to narrow down the static type from a general type (node()) to a more specific type (element()). It doesn't change the dynamic type. cast as, on the other hand, is used to convert an item from one type to another, changing both the static and dynamic types (e.g., xs:string to xs:boolean). It makes sense that cast as can only be used with atomic values (and not nodes), because what would it mean to convert an attribute to an element (etc.)? And there's no such thing as converting a node() item to an element() item, because there's no such thing as a node() item. node() only exists as a static union type. Moral of the story? Avoid XQuery processors that use static type checking. (Sorry for the snarky conclusion; I feel I've earned the right. :-) )
NEW ANSWER BASED ON UPDATED INFORMATION: It sounds like static type checking is a red herring (a big fat one). I believe you are in fact not dealing with an element but a document node, which is the invisible root node that contains the top-level element (document element) in the XPath data model representation of a well-formed XML document.
The tree is thus modeled like this:
[document-node]
|
<docElement>
|
<subelement>
and not like this:
<docElement>
|
<subelement>
I had assumed you were passing the <docElement> node. But if I'm right, you were actually passing the document node (its parent). Since the document node is invisible, its serialization (what you copied and pasted) is indistinguishable from an element node, and the distinction was lost when you pasted what is now interpreted as a bare element constructor in your XQuery. (To construct a document node in XQuery, you have to wrap the element constructor with document{ ... }.)
The instance of test fails because the node is not an element but a document-node. (It's not a node() per se, because there's no such thing; see explanation above.)
Also, this would explain why data() returns empty when you tried to get the <subelement> child of the document node (after relaxing the function argument type to node()). The first tree representation above shows that <subelement> is not a child of the document node; thus it returns the empty sequence.
Now for the solution. Before passing the (document node) parameter, get its element child (the document element), by appending /* (or /element() which is equivalent) like this:
let $parameter := someNamespace:functionX()/*
return local:myFunction($parameter)
Alternatively, let your function take a document node and update the argument you pass to data():
declare function local:myFunction($arg1 as document-node()) as element() {
let $value := data($arg1/*/subelement)
etc...
};
Finally, it looks like the description of eXist's request:get-data() function is perfectly consistent with this explanation. It says: "If its not a binary document, we attempt to parse it as XML and return a document-node()." (emphasis added)
Thanks for the adventure. This turned out to be a common XPath gotcha (awareness of document nodes), but I learned a few things from our detour into static type checking.
This works perfectly using Saxon 9.3:
declare namespace my = "my:my";
declare namespace their = "their:their";
declare function my:fun($arg1 as element()) as element()
{
$arg1/a
};
declare function their:fun2($arg1 as node()) as node()
{
$arg1
};
my:fun(their:fun2(/*) )
when the code above is applied on the following XML document:
<t>
<a/>
</t>
the correct result is produced with no error messages:
<a/>
Update:
The following should work even with the most punctuential static type-checking XQuery implementation:
declare namespace my = "my:my";
declare namespace their = "their:their";
declare function my:fun($arg1 as element()) as element()
{
$arg1/a
};
declare function their:fun2($arg1 as node()) as node()
{
$arg1
};
let $vRes := their:fun2(/*)
(: this prevents our code from runtime crash :)
return if($vRes instance of element())
then
(: and this assures the static type-checker
that the type is element() :)
my:fun(their:fun2(/*) treat as element())
else()
node() is an element, attribute, processing instruction, text node, etc.
But data() converts the result to a string, which isn't any of those; it's a primitive type.
You might want to try item(), which should match either.
See 2.5.4.2 Matching an ItemType and an Item in the W3C XQuery spec.
Although it's not shown in your example code, I assume you are actually returning a value (like the $value you are working with) from the local:myFunction.