Servicestack autoquery custom convention doesn't work with PostgreSQL

Question

I have defined new implicit convention

autoQuery.ImplicitConventions.Add("%WithinLastDays", "{Field} > NOW() - INTERVAL '{Value} days'");

The problem is that for postgres connection the query is wrong translated into

WHERE "TABLE"."FIELD" > NOW() - INTERVAL ':0 days'

and it doesn't send parameter to database. In case of built in conventions it works fine.

UPDATE

I was trying to define EndsWithConvention but there is the same issue - parameter is not passed to pgsql engine (however it is available in SqlExpression)

    autoQuery.EndsWithConventions
.Add("WithinLastDays", new QueryDbFieldAttribute() { Template= "{Field} >=  CURRENT_DATE - {Value}", ValueFormat= "interval '{0} days ago'" });

    autoQuery.EndsWithConventions
.Add("WithinLastDays", new QueryDbFieldAttribute() { Template= "{Field} >=  CURRENT_DATE - interval '{Value}'", ValueFormat= "{0} days ago" });

UPDATE 2 The below definition results in PostgresException: 42601: błąd składni w lub blisko "$1" (sorry for error in Polish)

autoQuery.EndsWithConventions.Add("WithinLastDays", new QueryDbFieldAttribute() { Template= "{Field} >=  CURRENT_DATE - interval {Value}", ValueFormat= "{0} days ago" });

The generated query is

  SELECT here columns
        FROM table
        WHERE table."publication_date" >=  CURRENT_DATE - interval $1
        LIMIT 100

UPDATE 3

autoQuery.EndsWithConventions.Add("WithinLastDays", new QueryDbFieldAttribute() { Template= "{Field} >=  CURRENT_DATE - {Value}", ValueFormat= "interval {0} 'days ago'" });

generates

SELECT ...
    FROM ...
    WHERE ...."publication_date" >=  CURRENT_DATE - $1

and issue PostgresException: 42883: operator doesn't exist: date - text

this is the dto definition

[Route("/search/tenders")]
    public class FindTenders : QueryDb<TenderSearchResult>
    {
        public int? PublicationDateWithinLastDays { get; set; }
    }

model:

public class EntitiySearchResult
{
    public DateTime PublicationDate { get; set; }
}

FINAL SOLUTION @mythz solved the registration problem and issue in using interval clause in my original query. The below definition works fine to get records within X days in the past from now. Thanks @mythz

  var autoQuery = new AutoQueryFeature() { MaxLimit = 100 };
            autoQuery.EndsWithConventions.Add("WithinLastDays", new QueryDbFieldAttribute
            {
                Template = "{Field} >= CURRENT_DATE + {Value}::interval",
                ValueFormat = "{0} days ago"
            });

Answer 1

The {Value} is replaced with a db parameter, if you want to change the value of the db parameter you need to use ValueFormat, e.g. ValueFormat="{0} days".

To define ValueFormat format an implicit convention you need to register an EndsWithConventions, e.g:

autoQuery.EndsWithConventions.Add("WithinLastDays", new QueryDbFieldAttribute { 
    Template= "{Field} >= CURRENT_DATE + {Value}::interval", 
    ValueFormat= "{0} days ago" 
});

Also note you likely want CURRENT_DATE + interval not -.