Wrapper to allow {@link SpanQuery} objects participate in composite single-field SpanQueries by 'lying' about their search field. That is, the masked SpanQuery will function as normal, but {@link SpanQuery#getField()} simply hands back the value supplied in this class's constructor.
This can be used to support Queries like {@link SpanNearQuery} or {@link SpanOrQuery} across different fields, which is not ordinarily permitted.
This can be useful for denormalized relational data: for example, when indexing a document with conceptually many 'children':
teacherid: 1 studentfirstname: james studentsurname: jones teacherid: 2 studenfirstname: james studentsurname: smith studentfirstname: sally studentsurname: jones
a SpanNearQuery with a slop of 0 can be applied across two {@link SpanTermQuery} objects as follows:
SpanQuery q1 = new SpanTermQuery(new Term("studentfirstname", "james")); SpanQuery q2 = new SpanTermQuery(new Term("studentsurname", "jones")); SpanQuery q2m new FieldMaskingSpanQuery(q2, "studentfirstname"); Query q = new SpanNearQuery(new SpanQuery[]{q1, q2m}, -1, false); to search for 'studentfirstname:james studentsurname:jones' and find teacherid 1 without matching teacherid 2 (which has a 'james' in position 0 and 'jones' in position 1). Note: as {@link #getField()} returns the masked field, scoring will be done using the norms of the field name supplied. This may lead to unexpected scoring behaviour.
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