meta-keyword.md

The META() function

For every document Couchbase Server will also store another document containing the meta data describing that document. Meta-data includes the following fields:

• Id - the primary key for the document
• CAS - Compare and Swap value
• Flags - SDK specific type encoding (internal use only)
• Type - the type of document stored in Couchbase (will always be JSON for N1QL)

There is additionally meta-data stored within couchbase for each document (TTL and Sequence Number), but this is not available from the META function.

META() example

The simplest usage of the META() function is to query it directly:

var query = (from meta in context.Query<DocumentMetadata>()
             select N1QlFunctions.Meta(meta)).
			 Take(1);

In this example, we are simply retrieving the meta-data from the first document returned in the beer-sample bucket. The "raw" results would look something like this:

{
    ...

    "results": [
        {
             {
                "cas": 1.4454516563790397e+18,
                "flags": 0,
                "id": "21st_amendment_brewery_cafe-south_park_blonde",
                "type": "json"
            }
        }
    ]

    ...
}

Here is another example where you want to return the meta-data along with a field from a document and create a projection that combines the two:

 var beers = (from b in context.Query<Beer>()
              where b.Type == "beer"
              select new {name = b.Name, meta = N1QlFunctions.Meta(b)});

And another example where you only want to return the "id" portion of the meta-data in your projection:

var beers = (from b in context.Query<Beer>()
             where b.Type == "beer"
             select new {name = b.Name, id = N1QlFunctions.Meta(b).Id});

The important thing to remember about the META function is that it is another tool available to you use in your queries!