Further br fixes

splink/analyse_blocking.py

@@ -8,7 +8,7 @@
 from .blocking import BlockingRule, _sql_gen_where_condition, block_using_rules_sqls
 from .misc import calculate_cartesian, calculate_reduction_ratio
 from .pipeline import CTEPipeline
-from .vertically_concatenate import compute_df_concat
+from .vertically_concatenate import compute_df_concat, enqueue_df_concat
 
 # https://stackoverflow.com/questions/39740632/python-type-hinting-without-cyclic-imports
 if TYPE_CHECKING:
@@ -258,3 +258,19 @@ def count_comparisons_from_blocking_rule_pre_filter_conditions_sqls(
     sqls.append({"sql": sql, "output_table_name": "__splink__total_of_block_counts"})
 
     return sqls
+
+
+def count_comparisons_from_blocking_rule_pre_filter_conditions(
+    linker: "Linker", blocking_rule: Union[str, "BlockingRule"]
+):
+    pipeline = CTEPipeline()
+    pipeline = enqueue_df_concat(linker, pipeline)
+
+    sqls = count_comparisons_from_blocking_rule_pre_filter_conditions_sqls(
+        linker, blocking_rule
+    )
+    pipeline.enqueue_list_of_sqls(sqls)
+
+    df_res = linker.db_api.sql_pipeline_to_splink_dataframe(pipeline)
+    res = df_res.as_record_dict()[0]
+    return int(res["count_of_pairwise_comparisons_generated"])

splink/find_brs_with_comparison_counts_below_threshold.py

@@ -6,7 +6,12 @@
 
 import pandas as pd
 
+from .analyse_blocking import (
+    count_comparisons_from_blocking_rule_pre_filter_conditions,
+)
 from .blocking import BlockingRule
+from .blocking_rule_creator import BlockingRuleCreator
+from .blocking_rule_library import CustomRule, block_on
 from .input_column import InputColumn
 
 if TYPE_CHECKING:
@@ -64,30 +69,13 @@ def _generate_blocking_rule(
     """Generate a Splink blocking rule given a list of column names which
     are provided as as string"""
 
-    # TODO: Refactor in Splink4
-    dialect = linker._sql_dialect
-
-    module_mapping = {
-        "presto": "splink.athena.blocking_rule_library",
-        "duckdb": "splink.duckdb.blocking_rule_library",
-        "postgres": "splink.postgres.blocking_rule_library",
-        "spark": "splink.spark.blocking_rule_library",
-        "sqlite": "splink.sqlite.blocking_rule_library",
-    }
-
-    if dialect not in module_mapping:
-        raise ValueError(f"Unsupported SQL dialect: {dialect}")
-
-    module_name = module_mapping[dialect]
-    block_on_module = __import__(module_name, fromlist=["block_on"])
-    block_on = block_on_module.block_on
-
     if len(cols_as_string) == 0:
-        return block_on("1")
+        br: BlockingRuleCreator = CustomRule("1=1", linker._sql_dialect)
+    else:
 
-    br = block_on(cols_as_string)
+        br = block_on(*cols_as_string)
 
-    return br
+    return br.get_blocking_rule(linker._sql_dialect)
 
 
 def _search_tree_for_blocking_rules_below_threshold_count(
@@ -165,8 +153,9 @@ def _search_tree_for_blocking_rules_below_threshold_count(
         return results  # All fields included, meaning we're at a leaf so exit recursion
 
     br = _generate_blocking_rule(linker, current_combination)
-    comparison_count = (
-        linker._count_num_comparisons_from_blocking_rule_pre_filter_conditions(br)
+
+    comparison_count = count_comparisons_from_blocking_rule_pre_filter_conditions(
+        linker, br
     )
 
     already_visited.add(frozenset(current_combination))

splink/linker.py

@@ -33,7 +33,7 @@
     truth_space_table_from_labels_table,
 )
 from .analyse_blocking import (
-    count_comparisons_from_blocking_rule_pre_filter_conditions_sqls,
+    count_comparisons_from_blocking_rule_pre_filter_conditions,
     cumulative_comparisons_generated_by_blocking_rules,
     number_of_comparisons_generated_by_blocking_rule_post_filters_sql,
 )
@@ -2787,7 +2787,7 @@ def count_num_comparisons_from_blocking_rule(
 
     def _count_num_comparisons_from_blocking_rule_pre_filter_conditions(
         self,
-        blocking_rule: BlockingRule,
+        blocking_rule: BlockingRuleCreator | str | dict,
     ) -> int:
         """Compute the number of pairwise record comparisons that would be generated by
         a blocking rule, prior to any filters (non equi-join conditions) being applied
@@ -2803,17 +2803,12 @@ def _count_num_comparisons_from_blocking_rule_pre_filter_conditions(
             int: The number of comparisons generated by the blocking rule
         """
 
-        pipeline = CTEPipeline()
-        pipeline = enqueue_df_concat(self, pipeline)
-
-        sqls = count_comparisons_from_blocking_rule_pre_filter_conditions_sqls(
-            self, blocking_rule
+        blocking_rule_obj = to_blocking_rule_creator(blocking_rule).get_blocking_rule(
+            self._sql_dialect
+        )
+        return count_comparisons_from_blocking_rule_pre_filter_conditions(
+            self, blocking_rule_obj
         )
-        pipeline.enqueue_list_of_sqls(sqls)
-
-        df_res = self.db_api.sql_pipeline_to_splink_dataframe(pipeline)
-        res = df_res.as_record_dict()[0]
-        return int(res["count_of_pairwise_comparisons_generated"])
 
     def cumulative_comparisons_from_blocking_rules_records(
         self,