Add QueryBuilder method for DataId-based WHERE expressions.

python/lsst/daf/butler/sql/queryBuilder.py

@@ -280,6 +280,37 @@ def whereParsedExpression(self, expression, op=and_):
             _LOG.debug("where from expression: %s", sqlExpression)
             self.whereSqlExpression(sqlExpression, op=op)
 
+    def whereDataId(self, dataId, op=and_):
+        """Add a dimension constraint from a data ID to the query's WHERE
+        clause.
+
+        All data ID values that correspond to dimension values already included
+        in the query will be used in the constraint; any others will be
+        ignored.
+
+        Parameters
+        ----------
+        dataId : `DataId` or `dict`
+            Data ID to require (at least partial) dimension equality with.
+        op : `sqlalchemy.sql.operator`
+            Binary operator to use if a WHERE expression already exists.
+
+        Returns
+        -------
+        links : `set` of `str`
+            The data ID keys actually used in the constraint.
+        """
+        links = set()
+        terms = []
+        for key, value in dataId.items():
+            selectable = self.findSelectableForLink(key)
+            if selectable is not None:
+                links.add(key)
+                terms.append(selectable.column[key] == value)
+        if terms:
+            self.whereSqlExpression(and_(terms), op=op)
+        return links
+
     def selectDimensionLink(self, link):
         """Add a dimension link column to the SELECT clause of the query.