Toolkit - Criteria for Dynamic Queries

This post if part of a series about the File System Toolkit - a custom content delivery API for SDL Tridion.

In the previous post Dynamic Content Queries, I presented a Query class that performs CustomMeta queries on JSON models published to the file system. This post presents the logic that actually queries for results and applies different boolean operators for different Criteria.

The base class for each criteria is Criterion, which defines the base methods each criteria must implement:

public abstract class Criterion {
    public Set<String> executeQuery() {
        return executeQuery(FilterImpl.EMPTY_FILTER);
    }

    public abstract Set<String> executeQuery(Filter filter);
}

The Filter class contains a set of allowed Publication ids, the item type and whether to include the range boundaries or not. The Filter is used in modifying the results retrieved for each criteria from the indexes.

Each criteria uses an index to lookup values associated to a given key. For example, a CustomMetaCriterion uses a key and value to retrieve all ComponentMeta or PageMeta that have a CustomMeta on that key with the specified value.

In order to do this lookup in a performant manner, there is an index where all keys and values are available (in ascending order) and by simply looking up an key-value tuple, we can retrieve the associated TcmUris of all items that have such key-value as CustomMeta. More information about these indexes is available in post Writing My Own Database Engine.

The CustomMetaCriterion uses the DateIndex, NumericIndex or StringIndex to lookup custom meta keys, depending on the type of the custom meta value (date, numeric or string).

In its simplest form, for a Key-StringValue CustomMeta, the executeQuery method builds an index key on the CustomMeta key and StringValue, then performs the StringIndex lookup for such key.

The result is a set of Strings representing the TcmUris that correspond to that index key in the StringIndex.

public Set<String> executeQuery(Filter filter) {
    String indexKey = stringIndex.buildKey(key, valueString);
    return new TreeSet<>(stringIndex.get(indexKey, filter));
}

The logical criteria (AndCriteria, OrCriteria) delegate their executeQuery to all sub-criteria and perform a logical intersection or union on the result sets. For example below, the AndCriteria below contains a list of sub-criteria that it needs to perform a logical AND between the result sets of each sub-criteria. As such, AndCriteria loops over the sub-criteria and then intersects their result sets:

public Set<String> executeQuery(Filter filter) {
    Set<String> result = null;
    boolean first = true;

    for (Criterion criterion : criteria) {
        Set<String> criterionResult = criterion.executeQuery(filter);

        if (first) {
            first = false;
            result = new TreeSet<>(criterionResult);
        } else {
            result.retainAll(criterionResult);
        }
    }

    return result;
}