Examples of org.geotools.filter.visitor.CapabilitiesFilterSplitter

org.geotools.filter.visitor.CapabilitiesFilterSplitter
Determines what queries can be processed server side and which can be processed client side.
IMPLEMENTATION NOTE: This class is implemented as a stack processor. If you're curious how it works, compare it with the old SQLUnpacker class, which did the same thing using recursion in a more straightforward way.

Here's a non-implementors best-guess at the algorithm: Starting at the top of the filter, split each filter into its constituent parts. If the given FilterCapabilities support the given operator, then keep checking downwards.

The key is in knowing whether or not something "down the tree" from you wound up being supported or not. This is where the stacks come in. Right before handing off to accept() the sub- filters, we count how many things are currently on the "can be proccessed by the underlying datastore" stack (the preStack) and we count how many things are currently on the "need to be post- processed" stack.

After the accept() call returns, we look again at the preStack.size() and postStack.size(). If the postStack has grown, that means that there was stuff down in the accept()-ed filter that wasn't supportable. Usually this means that our filter isn't supportable, but not always. In some cases a sub-filter being unsupported isn't necessarily bad, as we can 'unpack' OR statements into AND statements (DeMorgans rule/modus poens) and still see if we can handle the other side of the OR. Same with NOT and certain kinds of AND statements.

In addition this class supports the case where we're doing an split in the middle of a client-side transaction. I.e. imagine doing a against a WFS-T where you have to filter against actions that happened previously in the transaction. That's what the ClientTransactionAccessor interface does, and this class splits filters while respecting the information about deletes and updates that have happened previously in the Transaction. I can't say with certainty exactly how the logic for that part of this works, but the test suite does seem to test it and the tests do pass.

Since GeoTools 8.0, the {@link ClientTransactionAccessor} interface can also be used to instructthe splitter that a filter referencing a given {@link PropertyName} can't be encoded by theback-end, by returning {@link Filter#EXCLUDE} in{@link ClientTransactionAccessor#getUpdateFilter(String) getUpdateFilter(String)}. This is so because there may be the case where some attribute names are encodable to the back-end's query language, while others may not be, or may not be part of the stored data model. In such case, returning {@code Filter.EXCLUDE} makes the filter referencing the property name part of thepost-processing filter instead of the pre-processing filter. @author dzwiers @author commented and ported from gt to ogc filters by saul.farber @author ported to work upon {@code org.geotools.filter.Capabilities} by Gabriel Roldan @source $URL$ @since 2.5.3

     * @return a two-element array where the first element is the supported filter and the second
     *         the one to post-process
     * @see WSStrategy#splitFilters(WS_Protocol, Filter)
     */
    public Filter[] splitFilters(Capabilities caps, Filter queryFilter) {
        CapabilitiesFilterSplitter splitter = new CapabilitiesFilterSplitter(caps, null, null);


        queryFilter.accept(splitter, null);


        Filter server = splitter.getFilterPre();
        Filter post = splitter.getFilterPost();


        return new Filter[] { server, post };
    }

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        if (!fidFilter.getIdentifiers().isEmpty()) {
            server = fidFilter;
            post = Filter.EXCLUDE.equals(filter) ? Filter.INCLUDE : filter;
        } else {


            CapabilitiesFilterSplitter splitter = new CapabilitiesFilterSplitter(filterCaps, null,
                    null);


            filter.accept(splitter, null);
            server = splitter.getFilterPre();
            post = splitter.getFilterPost();


        }
        return new Filter[] { server, post };
    }

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            // server supports ID Filters so we need to check our queryFilter is valid            
            
            Capabilities idFilterCaps = new Capabilities();
            idFilterCaps.addName("Id");
            
            CapabilitiesFilterSplitter splitter = new CapabilitiesFilterSplitter(idFilterCaps, null, null);
            queryFilter.accept(splitter, null);
        
            Filter server = splitter.getFilterPre();
            if (server.equals(Filter.INCLUDE)) {
                // ID Filters not found in the root Filter
                // remove ID Filter from Capabilities
                FilterCapabilities filterCapabilitiesWithoutId = new FilterCapabilitiesImpl(
                        filterCapabilities.getVersion(),
                        filterCapabilities.getScalarCapabilities(),
                        filterCapabilities.getSpatialCapabilities(),
                        null,
                        filterCapabilities.getTemporalCapabilities());


                Capabilities capabilitiesWithoutId = new Capabilities();
                capabilitiesWithoutId.addAll(filterCapabilitiesWithoutId);
                
                return splitFilters(capabilitiesWithoutId, queryFilter);                
            } else {
                // ID Filter found
                // query the server using the ID Filter
                Filter post = splitter.getFilterPost();
                return new Filter[] { server, post };                            
            }
        } else {
            CapabilitiesFilterSplitter splitter = new CapabilitiesFilterSplitter(caps, null, null);


            queryFilter.accept(splitter, null);


            Filter server = splitter.getFilterPre();
            Filter post = splitter.getFilterPost();


            return new Filter[] { server, post };
        }
    }

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                return null;
            }
        };
        


        CapabilitiesFilterSplitter filterSplitter;
        filterSplitter = new CapabilitiesFilterSplitter(fcs, parent, transactionAccessor);


        final Filter filter = (Filter) this.originalFilter.accept(filterSimplifier, null);
        filter.accept(filterSplitter, null);


        Filter supported = filterSplitter.getFilterPre();
        Filter unsupported = filterSplitter.getFilterPost();
        Filter demultipliedFilter = (Filter) supported.accept(new LiteralDemultiplyingFilterVisitor(), null);
        this.supportedFilter = (Filter) demultipliedFilter.accept(filterSimplifier, null);
        this.unsupportedFilter = (Filter) unsupported.accept(filterSimplifier, null);
        
        StringBuilder whereClause = new StringBuilder();

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