refactor: rename Diagram.preview() to counts()

Avoids confusion with QueryExpression.preview() which shows table
contents. Diagram.counts() returns row counts per table.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/diagram.py

@@ -4,7 +4,7 @@
 This module provides the Diagram class for constructing derived views of the
 dependency graph. Diagram supports set operators (+, -, *) for selecting subsets
 of tables, restriction propagation (cascade, restrict) for selecting subsets of
-data, and inspection (preview, prune) for viewing those selections.
+data, and inspection (counts, prune) for viewing those selections.
 
 Mutation operations (delete, drop) live in Table, which uses Diagram internally
 for graph computation.
@@ -607,9 +607,9 @@ def _apply_propagation_rule(
 
         self._restriction_attrs.setdefault(child_node, set()).update(child_attrs)
 
-    def preview(self):
+    def counts(self):
         """
-        Show affected tables and row counts without modifying data.
+        Return affected row counts per table without modifying data.
 
         Returns
         -------

src/datajoint/table.py

@@ -1014,7 +1014,7 @@ def delete(
         diagram = diagram.cascade(self, part_integrity=part_integrity)
 
         if dry_run:
-            return diagram.preview()
+            return diagram.counts()
 
         conn = self.connection
         prompt = conn._config["safemode"] if prompt is None else prompt

tests/integration/test_erd.py

@@ -110,10 +110,10 @@ def test_prune_after_restrict(schema_simp_pop):
     """Prune after restrict removes tables with zero matching rows."""
     diag = dj.Diagram(schema_simp_pop, context=LOCALS_SIMPLE)
     restricted = diag.restrict(A & "id_a=0")
-    counts = restricted.preview()
+    counts = restricted.counts()
 
     pruned = restricted.prune()
-    pruned_counts = pruned.preview()
+    pruned_counts = pruned.counts()
 
     # Every table in pruned preview should have > 0 rows
     assert all(c > 0 for c in pruned_counts.values()), "pruned diagram should have no zero-count tables"
@@ -128,10 +128,10 @@ def test_prune_after_cascade(schema_simp_pop):
     """Prune after cascade removes tables with zero matching rows."""
     diag = dj.Diagram(schema_simp_pop, context=LOCALS_SIMPLE)
     cascaded = diag.cascade(A & "id_a=0")
-    counts = cascaded.preview()
+    counts = cascaded.counts()
 
     pruned = cascaded.prune()
-    pruned_counts = pruned.preview()
+    pruned_counts = pruned.counts()
 
     assert all(c > 0 for c in pruned_counts.values())
 
@@ -159,9 +159,9 @@ def test_prune_then_restrict(schema_simp_pop):
     further = pruned.restrict(A & "id_a=0")
 
     # Should not raise; further restriction should narrow results
-    counts = further.preview()
+    counts = further.counts()
     assert all(c >= 0 for c in counts.values())
     # Tighter restriction should produce fewer or equal rows
-    pruned_counts = pruned.preview()
+    pruned_counts = pruned.counts()
     for table in counts:
         assert counts[table] <= pruned_counts.get(table, 0)