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Executing Functions

Functions can be executed to provide sets of features or data.

Execute a function

The path /functions/{funid}/items is the basic query to execute a function and return the set of features or data it produces.

The response from a spatial function is a GeoJSON feature collection containing the result. The response from a non-spatial function is a JSON dataset containing the result.

These are similar to using SQL statement clauses to control the results of a query. In fact, the service implements these parameters by generating the equivalent SQL. However, these filters are applied to the results of an executed function, so it doesn’t necessarily allow optimizing the execution of the function. (For example, specifying a bounding box only filters the results generated by the function; it is not available to the function to reduce the number of records generated.)

Function arguments

Functions provide query parameters of the form param=arg-value to provide an argument value for each function parameter. Omitted parameters use the default specified in the function definition (if any). If a function parameter does not provide a default then a value must be supplied.

Example

http://localhost:9000/functions/countries_name/items?name_prefix=T

Filter by bounding box

The query parameter bbox=MINX,MINY,MAXX,MAXY is used to limit the features returned to those that intersect a specified bounding box. The bounding box is specified in geographic coordinates (longitude/latitude, SRID = 4326). If the source data has a non-geographic coordinate system the bounding box is transformed to the source coordinate system to perform the query.

This parameter is only useful for spatial functions.

Example

http://localhost:9000/functions/countries_name/items?bbox=10.4,43.3,26.4,47.7

Specify response properties

The query parameter properties=PROP1,PROP2,PROP3... specifies the properties returned in the response. This reduces the response size of functions that produce a large number of records.

Example

http://localhost:9000/functions/countries_name/items?properties=name

Limiting and paging

The query parameter limit=N can controls the maximum number of data items returned in a response.

The query parameter offset=N specifies the offset in the actual query result at which the response data set starts.

When used together, these two parameters allow paging through large result sets.

Example

http://localhost:9000/functions/countries_name/items?limit=50&offset=200

The default page size and the maximum page size are set by the configuration parameters LimitDefault and LimitMax.

Ordering

The result set can be ordered by any property it contains. This allows performing “greatest N” or “smallest N” queries.

  • orderBy=PROP orders results by PROP in ascending order

The sort order can be specified by appending :A (ascending) or :D (descending) to the ordering property name. The default is ascending order.

  • orderBy=PROP:A orders results by PROP in ascending order
  • orderBy=PROP:D orders results by PROP in descending order

Example

http://localhost:9000/functions/countries_name/items?orderBy=name