org.lockss.laaws.poller.impl.package-info Maven / Gradle / Ivy
/**
SQL-Like Query
There are several operations that require as an argument a text string
containing a SQL-like query used to determine the results to be returned.
The result of executing such a query is always a List of objects. The kind
of objects populating the result List is specific to the web service operation
being performed.
For example, the Daemon Status web service operation {@link
org.lockss.ws.status.DaemonStatusService#queryPlugins(java.lang.String)
queryPlugins} returns a List of {@link org.lockss.ws.entities.PluginWsResult}
objects.
The query may have up to three clauses, each of them allowing the user to
control a different aspect of the results. Each clause is separated from the
other by at least one space.
The three clauses are, in order of appearance in the query:
- A required select clause, which specifies which properties in the
returned objects should be properly populated, while the rest are populated
with null values.
The text of the select clause begins with the word
SELECT followed by a space and either a comma-separated list of
property names or an asterisk (*):
- If a list of property names is included, the names in the list must
correspond to properties of the objects being returned. The property names
may be obtained from the get* accessor method names by removing the leading
"get" and changing the capitalization of the resulting first letter to
lower case.
- The asterisk (
*) is a shorthand way of specifying all the
property names.
- An optional where clause, which specifies which objects have to be
included in the results, while the rest are not.
The text of the where clause begins with the word WHERE
followed by a space and a space-separated list of conditions using
OR and AND keywords to specify the filtering logic.
Parentheses may be used in the typical grouping manner.
Each condition is a comparison between properties of the objects being
returned and other properties or between properties and constants using
comparators like <, =, etc. Text constants must
be surrounded by single quote (') characters.
- An optional order by clause, which specifies the order of the
objects in the List that contains the results.
The text of the order by clause begins with the words
ORDER BY followed by a space and a comma-separated list of
property names, each of them optionally followed by the keyword
ASC (default) or DESC.
Examples
select *: It is the simplest (but costly) query and it
results in a List of all the objects with each and every property properly
populated.
select name: Results in a List of all the objects with just
the name property properly populated and the rest of properties
populated with null values.
select name where id > 10: Results in a List of the
objects with the numeric id property greater than 10 only
and properly populated with just the name property and the rest
of properties populated with null values.
select id where name = 'abc': Results in a List of the
objects with the text name property equal to abc only and
properly populated with just the id property and the rest of
properties populated with null values.
select id, name where value < 100 and color like 'red%' order by
id: Results in a List of the objects with both the numeric
value property lower than 100 and the text
color property starting with red only and properly
populated with just the id and name properties and
the rest of properties populated with null values. The objects in the list are
ordered from the smallest id property to the largest one.
select id, longValue where toDate(longValue) <
toDate('02/Apr/2014'): Results in a List of the objects with the long
numeric longValue property representing a date before
April 2, 2014 and properly populated with just the id and
longValue properties and the rest of properties populated with
null values.
*/
package org.lockss.laaws.poller.impl;