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From "Eric Evans (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-2025) generalized way of expressing hierarchical values
Date Tue, 25 Jan 2011 21:01:46 GMT


Eric Evans commented on CASSANDRA-2025:

I agree, I think there are two reasons to use escaping:

1.  It's necessary to deal with an unforeseen ambiguity
2.  It's reserved for exceptional situations, and where a cure would be worse than the disease.

#1 could happen from failing to plan ahead, but probably most often occurs when a spec is
(re)used in ways that weren't originally taken into consideration (in which case _unforseeable_
is probably more accurate).

The best example of #2 I can think of would be your shell. It tokenizes on whitespace, which
means that you have to escape any whitespace character that is part of a token.  Whitespace
in tokens though is exceptional, and any other delimiter would border on the obscene.

I don't think the latter applies here, and I raised this ticket to avoid the former (if possible).

> generalized way of expressing hierarchical values
> -------------------------------------------------
>                 Key: CASSANDRA-2025
>                 URL:
>             Project: Cassandra
>          Issue Type: Sub-task
>          Components: API
>            Reporter: Eric Evans
>            Assignee: Eric Evans
>            Priority: Minor
>             Fix For: 0.8
>   Original Estimate: 0h
>  Remaining Estimate: 0h
> While hashing out {{CREATE KEYSPACE}}, it became obvious that we needed a syntax for
expressing hierarchical values.  Properties like {{replication_factor}} can be expressed simply
using keyword arguments like ({{replication_factor = 3}}), but {{strategy_options}} is a map
of strings.
> The solution I took in CASSANDRA-1709 was to dot-delimit "map name" and option key, so
for example:
> {code:style=SQL}
> CREATE KEYSPACE keyspace WITH ... AND strategy_options.DC1 = "1" ...
> {code}
> This led me to wonder if this was a general enough approach for any future cases that
might come up.  One example might be compound/composite column names.  Dot-delimiting is a
bad choice here since it rules out ever introducing a float literal.
> One suggestion would be to colon-delimit, so for example:
> {code:style=SQL}
> CREATE KEYSPACE keyspace WITH ... AND strategy_options:DC1 = "1" ...
> {code}
> Or in the case of composite column names:
> {code:style=SQL}
> SELECT columnA:columnB,column1:column2 FROM Standard2 USING CONSISTENCY.QUORUM WHERE
KEY = key;
> UPDATE Standard2 SET columnA:columnB = valueC, column1:column2 = value3 WHERE KEY = key;
> {code}
> As an aside, this also led me to the conclusion that {{CONSISTENCY.<LEVEL>}} is
probably a bad choice for consistency level specification.  It mirrors the underlying enum
for no good reason and should probably be changed to {{CONSISTENCY <LEVEL>}} (i.e. omitting
the separator).  For example:
> {code:style=SQL}
> {code}
> Thoughts?
> *Edit: improved final example*
> *Edit: restore final example, create new one (gah).*

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