Elasticsearch NEST: ordering terms aggregation with multiple criteria - elasticsearch

Using NEST, I need to be able to order a terms aggregation with multiple criteria (requires ElasticSearch 1.5 or later). For example:
"order": [{"avg_rank": "desc"}, {"avg_score": "desc"}]
This is working great using the raw JSON that I created to verify I was getting the expected behavior. Now, in trying to translate that over to code using the NEST library, I'm not seeing how that would be accomplished.
The OrderDescending() method has only one implementation that takes a string for the key. I need a C# "params" type method that can take a list of OrderDescending() and\or OrderAscending() elements.
Is there a way to do this in NEST that I'm overlooking?
Is there a way in NEST to work around this where I can inject a little raw JSON where I need it?
FWIW, I've been using the "fluent" style to create my queries.
EDIT:
I see that, using "object initializer" syntax, I could manually create the dictionary and add my criteria elements. Problem is, I have large amounts of code written in "fluent" syntax. So,
Is there a way to use an "object initializer" object and convert it to a "fluent" descriptor? In this case, a TermsAggregator to a TermsAggregationDescriptor?
EDIT 2:
I should have mentioned originally that I tried .OrderDescending("avg_rank").OrderDescending("avg_score") already. That simply took that last one in the chain. In looking at the code, I can see why. Each call to OrderDescending blindly news up the dictionary instead of checking to see if one was already newed up and adding a new key to the dictionary if it already exists.
Based on this, I believe this is a bug for which I have entered a report here:
OrderDescending and OrderAscending cannot be chained for multi-criteria ordering
EDIT 3:
I appreciate all the answers (some of which are getting deleted) because they're helping drive this along and are responsible for these edits. I should also have mentioned originally that I discovered that:
"order": { "avg_rank": "desc", "avg_score": "desc" }
does not work. I don't know why for sure but ES will only use the last one in that case. It has be a list of dictionaries as shown in my example above at the top. I've verified that correctly sub-orders the aggregation on the second element. So, the underlying object cannot be typed as a simple dictionary. I've also added this information to the bug report I created (as noted in EDIT 2).

If you're using the fluent syntax you can just chain the sorts together.
Sample:
var esClient = ninjectKernel.Get<IElasticClient>();
var query = esClient.Search<RedemptionES>(s=> s
.SortAscending(a=>a.Date)
.SortDescending(d=>d.Input.User.Name)
);
Response:
{
"sort": [
{
"#timestamp": {
"order": "asc"
}
},
{
"input.user.name": {
"order": "desc"
}
}
]
}

Martijn Laarman of the NEST team was very responsive and kind enough to provide a work around for the bug I reported in EDIT 2 of the description above. The fix can be found in the comments of that same bug report: Work around for NEST library multi-criteria aggregation ordering.
Note that he provided a work around for both object initializer and fluent syntaxes (the one I needed).

Related

get updated doc ids in Elasticsearch's update_by_query api

I use the following query to update some weight filed in matched docs. I need to get the list of updated docs id but I don't know how to do that?
POST v1_shingle_analyzer/_update_by_query
{
"script" : {
"source": "ctx._source.content_completion.weight ++",
"lang": "painless",
"_source":true,
"_source_includes":"_id"
},
"query": {
"ids": {
"values": ["ad22784cde0cecab176811ca9d77e7c2","dssdg784cde0cecab176811ca9fgdfg"]
}
}
}
References this, this legend answer, this plugin and few ES forum posts, JIRAs.
Short answer:
There is no direct way of doing this. You may need to query again with the IDs to check whether it changed.
Detailed answer:
As per the documentation, Response doesn't have a field to return the updated IDs.
The plugin mentioned is deprecated/dropped the support to context as per the GitHub link. But I think that
you can look at the source code to figure out a way to get the IDs updated If it really matters.
I see here that there is a response option. We can set three values. But it doesn't say anything about returning IDs. It says options related to which shard, what type is updated, etc.. You can look at this if there is anyway to tweak this.
Kindly let me know for more information.

Elasticsearch Dynamic Field Mapping and JSON Dot Notation

I'm trying to write logs to an Elasticsearch index from a Kubernetes cluster. Fluent-bit is being used to read stdout and it enriches the logs with metadata including pod labels. A simplified example log object is
{
"log": "This is a log message.",
"kubernetes": {
"labels": {
"app": "application-1"
}
}
}
The problem is that a few other applications deployed to the cluster have labels of the following format:
{
"log": "This is another log message.",
"kubernetes": {
"labels": {
"app.kubernetes.io/name": "application-2"
}
}
}
These applications are installed via Helm charts and the newer ones are following the label and selector conventions as laid out here. The naming convention for labels and selectors was updated in Dec 2018, seen here, and not all charts have been updated to reflect this.
The end result of this is that depending on which type of label format makes it into an Elastic index first, trying to send the other type in will throw a mapping exception. If I create a new empty index and send in the namespaced label first, attempting to log the simple app label will throw this exception:
object mapping for [kubernetes.labels.app] tried to parse field [kubernetes.labels.app] as object, but found a concrete value
The opposite situation, posting the namespaced label second, results in this exception:
Could not dynamically add mapping for field [kubernetes.labels.app.kubernetes.io/name]. Existing mapping for [kubernetes.labels.app] must be of type object but found [text].
What I suspect is happening is that Elasticsearch sees the periods in the field name as JSON dot notation and is trying to flesh it out as an object. I was able to find this PR from 2015 which explicitly disallows periods in field names however it seems to have been reversed in 2016 with this PR. There is also this multi-year thread from 2015-2017 discussing this issue but I was unable to find anything recent involving the latest versions.
My current thoughts on moving forward is to standardize the Helm charts we are using to have all of the labels use the same convention. This seems like a band-aid on the underlying issue though which is that I feel like I'm missing something obvious in the configuration of Elasticsearch and dynamic field mappings.
Any help here would be appreciated.
I opted to use the Logstash mutate filter with the rename option as described here:
https://www.elastic.co/guide/en/logstash/current/plugins-filters-mutate.html#plugins-filters-mutate-rename
The end result looked something like this:
filter {
mutate {
'[kubernetes][labels][app]' => '[kubernetes][labels][app.kubernetes.io/name]'
'[kubernetes][labels][chart]' => '[kubernetes][labels][helm.sh/chart]'
}
}
Although personally I've never encountered the exact same issue, I had similar problems when I indexed some test data and afterwards changed the structure of the document that should have been indexed (especially when "unflattening" data structures).
Your interpretation of the error message is correct. When you first index the document
{
"log": "This is another log message.",
"kubernetes": {
"labels": {
"app.kubernetes.io/name": "application-2"
}
}
}
Elasticsearch will recognize the app as an object/structure due to dynamic mapping.
When you then try to index the document
{
"log": "This is a log message.",
"kubernetes": {
"labels": {
"app": "application-1"
}
}
}
the previously, dynamically created mapping defined the field app as an object with sub-fields but elasticsearch encounters a concrete value, namely "application-1".
I suggest that you setup an index template to define the correct mappings. For the 'outdated' logging-versions I suggest to pre-process the particular documents either through an elasticsearch ingest-pipeline or with e.g. Logstash to get the documents in the correct format.
Hope that helps.

Use Graphql variables to define fields

I am trying to do something effectively like this
`query GetAllUsers($fields: [String]) {
users {
...$fields
}
}`
Where my client (currently Apollo for react) then passes in an array of fields in the variables section. The goal is to be able to pass in an array for what fields I want back, and that be interpolated to the appropriate graphql query. This currently returns a GraphQL Syntax error at $fields (expects a { but sees $ ). Is this even possible? Am I approaching this the wrong way?
One other option I had considered was invoking a JavaScript function and passing that result to query(), where the function would do something like the following:
buildQuery(fields) {
return gql`
query {
users {
${fields}
}
}`
}
This however feels like an unecessary workaround.
Comments summary:
Non standard requirements requires workarounds ;)
You can use fragments (for predefined fieldsets) but they probably won't be freely granular (field level).
Variables are definitely not for query definition (but for variables used in query).
Daniel's suggestion: gql-query-builder
It seams that graphQL community is great and full of people working on all possible use cases ... it's enough to search for solutions or ask on SO ;)

What are aliases in elasticsearch for?

I recently started working in a company that uses Elasticsearch. While most of its concepts are somewhat similar to relational databases and I am able to understand them, I still don't quite get the concept of aliases.
I did not find any such question here and the information provided on the Elasticsearch website did not help much either.
Can someone explain what aliases are for and ideally include an example of a situation where they are needed?
aliases are like soft links or shortcuts to actual indexes
the advantage is to be able to have an alias pointing to index1a while building or re-indexing on index2b and the moment of swapping them is atomic thanks to the alias, to which all code should point
Renaming an alias is a simple remove then add operation within the same API. This operation is atomic, no need to worry about a short period of time where the alias does not point to an index:
[EDIT] as pointed out #wholevinski aliases have other functionalities like:
Multiple indices can be specified for an action ...
all the info is in the page you have linked
[EDIT2] more on why the need/benefit of the atomicity
the key being "zero downtime" https://en.wikipedia.org/wiki/Zero_unscheduled_downtime or https://en.wikipedia.org/wiki/High_availability
https://www.elastic.co/guide/en/elasticsearch/guide/current/index-aliases.html
We will talk more about the other uses for aliases later in the book. For now we will explain how to use them to switch from an old index to a new index with zero downtime.
#arhak covered the topic pretty well.
One use case that (at least) made me understand the value of indices was the need to remove out-of-date documents and more specifically when using time-based-indices.
For example, you need to keep the logs of an application for at least one year. You decide to use time-based-indices, meaning you save into indices with the following format: 2018-02-logs, 2018-03-logs etc.. In order to be able to search in every index you create the following alias:
POST /_aliases
{
"actions": [{
"add": {
"alias": "current-logs", "indices": [ "2018-02-logs","2018-03-logs" ]
}
}]
}
And query like:
GET /current-logs/_search
Another advantage is that you can delete the out-of-date values very easily:
POST /_aliases
{
"actions": [
{ "remove": { "alias": "current-logs", "index": "logs_2018-01" }}
]
}
and DELETE /logs_2018-01
Aliases are basically created to group a set of indices and make them accessible regarless the name they have. Is a pointer to a set of indices. You can also apply a query/condition to all of these indices. It is very useful when performing queries or creating dashboards over the same group of indices all the time. In addition, if in the future you change the name of the indices that are part of an alias, the end users will not notice that change since it is for transparent for them and you will only update the pointer.

GraphQL "not equal" operator?

I have a GraphQl API for listing a bunch of items, and I can query it perfectly etc.
But now I'd like to query for a subset of that list where one property can have 'all possible values except one specific one'.
For example, I want to query something like this:
{
items(status: !"Unwanted"){
id
}
}
That exclamation mark obviously doesn't work, but it illustrates what I am after.
Can't find any information about this online.
Does anybody know of a way to do this?
I would really hate having to enumerate all possible wanted values instead of just excluding the one unwanted value. This would be really bad design and is not scalable.
Thanks.
Use ne :
{
items(filter: {status: {ne: "Unwanted"}}){
id
}
}
If you can define the schema (implement the server) then you can add a second argument like statusExcept to the items field. Then in the resolve method check if status or statusExcept was set and deliver the items according to that.
It the server API is fixed there is afaik nothing that you can do except getting everything and filter on the client.
Using GraphQL version 4.3.2 the syntax has changed and you will need to use notIn
{
items(filter: {status: {notIn: "Unwanted"}}){
id
}
}

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