Expose noop filter to users

[scrawfor]

It would be useful to expose the noop filter to users. This allows a filter to be "switched off" without removing the filter property from the json. This is useful when developing a query, or in tools which programmatically generate druid queries.

[jon-wei]

Thanks for the contribution, can you please sign the CLA?

http://druid.io/community/cla.html

[scrawfor]

Done.

[b-slim]

@scrawfor not sure how this is different from null filter but it is okay if you like reading noop instead.

[scrawfor]

@b-slim If by null filter you mean just removing the filter property, I think this has two small use cases.

1. We use a (limited) reporting tool which builds our JSON queries for us, which based on user input enables or disables filters. Without the noop filter, we have to check if any filter should be applied before adding a filter property. With the noop filter, we can just modify the type for each individual filter to make it inactive. It reduces the amount of logic we need to build when generating queries.

2. When developing a query, you can just disable a filter, instead of removing the filter property entirely. At least for me, this is preferable, because I know I've removed a filter and forgotten what I had in place.

"filter": {
    "type": "and",
    "fields": [{
      "type": "selector",
      "dimension": "profile",
      "value": "my_application"
    }, {
      "type": "selector",
      "dimension": "browser_name",
      "value": "Chrome"
    }]
  }

becomes

"filter": {
    "type": "noop",
    "fields": [{
      "type": "selector",
      "dimension": "profile",
      "value": "premierconnect"
    }, {
      "type": "selector",
      "dimension": "browser_name",
      "value": "Chrome"
    }]
  },

Now I can see what my results are without the filter, and I haven't made any large modifications to my query. If I want to re-enable my filter, I just change "noop" back to "and".

[niketh]

@scrawfor You can also change "filter" to "afilter" , it does the same thing :). But this is useful too, but you have to remember which filter you have replaced with noop

[scrawfor]

I've been running this in my cluster for a week or so, and just found a bug. If you change the type of a filter to noop inside of an and filter a NPE is thrown.

"filter": { "type": "and", "fields": [{ "type": "selector", "dimension": "my_dimension", "value": "some_value" }, {"type": "noop"}] },

throws

java.lang.NullPointerException at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:213) ~[guava-16.0.1.jar:?] at com.google.common.collect.ImmutableCollection$ArrayBasedBuilder.add(ImmutableCollection.java:339) ~[guava-16.0.1.jar:?] at com.google.common.collect.ImmutableList$Builder.add(ImmutableList.java:652) ~[guava-16.0.1.jar:?] at com.google.common.collect.ImmutableList$Builder.add(ImmutableList.java:630) ~[guava-16.0.1.jar:?] at com.google.common.collect.ImmutableCollection$Builder.addAll(ImmutableCollection.java:301) ~[guava-16.0.1.jar:?] at com.google.common.collect.ImmutableList$Builder.addAll(ImmutableList.java:691) ~[guava-16.0.1.jar:?] at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:275) ~[guava-16.0.1.jar:?] at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:226) ~[guava-16.0.1.jar:?] at io.druid.segment.filter.Filters.toFilters(Filters.java:84) ~[druid-processing-0.11.0.jar:0.11.0] at io.druid.query.filter.AndDimFilter.toFilter(AndDimFilter.java:75) ~[druid-processing-0.11.0.jar:0.11.0] at io.druid.segment.filter.Filters.toFilter(Filters.java:109) ~[druid-processing-0.11.0.jar:0.11.0]

Very unfamiliar with the project still, but to me the appropriate solution would be to remove any noop filters instead of trying to actually convert it to a filter. But I wanted to open it up and see if you guys had any input.

[b-slim]

@scrawfor IMO this noop filter is no sense i think what you are asking for is true filter that matchs everything and maybe false opposite of true. How about adding a filter of type true instead of exposing noop ?

[scrawfor]

I'm fine with that. It does better represent what we are actually doing. I only went with the noop because it already existed

Take a look and let me know if this is more like what you're thinking.

[b-slim]

Take a look and let me know if this is more like what you're thinking.

@scrawfor where ?

[scrawfor]

My bad. Wan't thinking that this wouldn't be updated. I created a new PR #5711