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https://issues.apache.org/jira/browse/SOLR-7377?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14512165#comment-14512165
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Dennis Gove commented on SOLR-7377:
-----------------------------------
I was thinking that all comparators, no matter their implemented comparison
logic, return one of three basic values when comparing A and B.
1. A and B are logically equal to each other
2. A is logically before B
3. A is logically after B
The implemented comparison logic is then wholly dependent on what one might be
intending to use the comparator for. For example, EqualToComparator's
implemented comparison logic will return that A and B are logically equal if
they are in fact equal to each other. Its logically before/after response
depends on the sort order (ascending or descending) but is basically deciding
if A is less than B or if A is greater than B.
One could, if they wanted to, create a comparator returning that two dates are
logically equal to each other if they occur within the same week. Or a
comparator returning that two numbers are logically equal if their values are
within the same logarithmic order of magnitude. So on and so forth.
My thinking is that comparators determine the logical comparison and make no
assumption on what that implemented logic is. This leaves open the possibility
of implementing other comparators for given situations as they arise.
> SOLR Streaming Expressions
> --------------------------
>
> Key: SOLR-7377
> URL: https://issues.apache.org/jira/browse/SOLR-7377
> Project: Solr
> Issue Type: Improvement
> Components: clients - java
> Reporter: Dennis Gove
> Priority: Minor
> Fix For: Trunk
>
> Attachments: SOLR-7377.patch
>
>
> It would be beneficial to add an expression-based interface to Streaming API
> described in SOLR-7082. Right now that API requires streaming requests to
> come in from clients as serialized bytecode of the streaming classes. The
> suggestion here is to support string expressions which describe the streaming
> operations the client wishes to perform.
> {code:java}
> search(collection1, q=*:*, fl="id,fieldA,fieldB", sort="fieldA asc")
> {code}
> With this syntax in mind, one can now express arbitrarily complex stream
> queries with a single string.
> {code:java}
> // merge two distinct searches together on common fields
> merge(
> search(collection1, q="id:(0 3 4)", fl="id,a_s,a_i,a_f", sort="a_f asc, a_s
> asc"),
> search(collection2, q="id:(1 2)", fl="id,a_s,a_i,a_f", sort="a_f asc, a_s
> asc"),
> on="a_f asc, a_s asc")
> // find top 20 unique records of a search
> top(
> n=20,
> unique(
> search(collection1, q=*:*, fl="id,a_s,a_i,a_f", sort="a_f desc"),
> over="a_f desc"),
> sort="a_f desc")
> {code}
> The syntax would support
> 1. Configurable expression names (eg. via solrconfig.xml one can map "unique"
> to a class implementing a Unique stream class) This allows users to build
> their own streams and use as they wish.
> 2. Named parameters (of both simple and expression types)
> 3. Unnamed, type-matched parameters (to support requiring N streams as
> arguments to another stream)
> 4. Positional parameters
> The main goal here is to make streaming as accessible as possible and define
> a syntax for running complex queries across large distributed systems.
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