CODEWITHSUNDEEP
google-app-engine
Vladimir Mihailenco
Vladimir Mihailenco

Reputation: 3382

GAE and Prospective search: empty query

I want to create prospective search subscription with empty query, but GAE raises exception

QuerySyntaxError: query:'' detail:'Query is empty.'

which is not compatible with Search API, which allows empty queries. Any workarounds? Should I file an issue?

Upvotes: 0

Views: 219

Answers (2)

bobwyman
bobwyman

Reputation: 21

The Prospective Search Service is intended to support applications that filter a stream of documents; applications that want less than all documents matched. In such an application, an "empty query" would normally be considered evidence of a bug. Admittedly, empty queries might sometimes be useful for various debugging purposes, however, the decision was made to design the interface's contracts with production use in mind.

As suggested by Will Brown, if you want a subscription that will match all documents, then insert some dummy field with a constant value into your documents and then create a query that matches just that field and value. Given that there is such an easy work-around available for those rare cases when "all documents" are needed, I think it unlikely that we would provide support for empty queries. It might also be interesting to note that the prohibition against empty queries is not just in the AppEngine code but also in the backend servers that AppEngine accesses to provide the Prospective Search Service.

Although the "Search API" (which really should be called the "Retrospective Search API") may support empty queries, it is important to realize that resource utilization patterns for prospective search are very, very different from those of retrospective search. For instance, you might have an application that is streaming hundreds of documents per second into both a document index (using retrospective search) and through a query index (using prospective seach). In such a system, an empty retrospective query is only going to return just a few documents whenever that query is submitted. On the other hand, a prospective query would generate a real-time stream of all documents. The presence of just a few prospective queries could thus generate significant loads on your application. In general, if you want a firehose, real-time push feed of everything published, it is best to code that up explicitly.

Upvotes: 2

Haldean Brown
Haldean Brown

Reputation: 12721

You can file a feature request for this, but it is by design (I don't know why). If you know that incoming documents will have something in common, you can write a query for those; for example, if you add a field "alldocuments" with content "yes" to the document when you send the request, you could register a query like "alldocuments:yes" to match all documents.

Upvotes: 1

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