change option to enum and add test

src/Core/Settings.h

@@ -612,7 +612,7 @@ class IColumn;
     M(UInt64, mutations_sync, 0, "Wait for synchronous execution of ALTER TABLE UPDATE/DELETE queries (mutations). 0 - execute asynchronously. 1 - wait current server. 2 - wait all replicas if they exist.", 0) \
     M(Bool, enable_lightweight_delete, true, "Enable lightweight DELETE mutations for mergetree tables.", 0) ALIAS(allow_experimental_lightweight_delete) \
     M(UInt64, lightweight_deletes_sync, 2, "The same as 'mutation_sync', but controls only execution of lightweight deletes", 0) \
-    M(String, lightweight_mutation_projection_mode, "throw", "When lightweight delete happens on a table with projection(s), the possible operations include throw the exception as projection exists, or drop all projection related to this table then do lightweight delete.", 0) \
+    M(LightweightMutationProjectionMode, lightweight_mutation_projection_mode, LightweightMutationProjectionMode::THROW, "When lightweight delete happens on a table with projection(s), the possible operations include throw the exception as projection exists, or drop all projection related to this table then do lightweight delete.", 0) \
     M(Bool, apply_deleted_mask, true, "Enables filtering out rows deleted with lightweight DELETE. If disabled, a query will be able to read those rows. This is useful for debugging and \"undelete\" scenarios", 0) \
     M(Bool, optimize_normalize_count_variants, true, "Rewrite aggregate functions that semantically equals to count() as count().", 0) \
     M(Bool, optimize_injective_functions_inside_uniq, true, "Delete injective functions of one argument inside uniq*() functions.", 0) \

src/Core/SettingsEnums.cpp

@@ -173,6 +173,10 @@ IMPLEMENT_SETTING_ENUM(ParallelReplicasCustomKeyFilterType, ErrorCodes::BAD_ARGU
     {{"default", ParallelReplicasCustomKeyFilterType::DEFAULT},
      {"range", ParallelReplicasCustomKeyFilterType::RANGE}})
 
+IMPLEMENT_SETTING_ENUM(LightweightMutationProjectionMode, ErrorCodes::BAD_ARGUMENTS,
+    {{"throw", LightweightMutationProjectionMode::THROW},
+     {"drop", LightweightMutationProjectionMode::DROP}})
+
 IMPLEMENT_SETTING_AUTO_ENUM(LocalFSReadMethod, ErrorCodes::BAD_ARGUMENTS)
 
 IMPLEMENT_SETTING_ENUM(ParquetVersion, ErrorCodes::BAD_ARGUMENTS,

src/Core/SettingsEnums.h

@@ -339,6 +339,14 @@ enum class ParallelReplicasCustomKeyFilterType : uint8_t
 
 DECLARE_SETTING_ENUM(ParallelReplicasCustomKeyFilterType)
 
+enum class LightweightMutationProjectionMode : uint8_t
+{
+    THROW,
+    DROP,
+};
+
+DECLARE_SETTING_ENUM(LightweightMutationProjectionMode)
+
 DECLARE_SETTING_ENUM(LocalFSReadMethod)
 
 enum class S3QueueMode : uint8_t

src/Interpreters/InterpreterDeleteQuery.cpp

@@ -116,15 +116,15 @@ BlockIO InterpreterDeleteQuery::execute()
         if (table->hasProjection())
         {
             auto context = Context::createCopy(getContext());
-            auto mode = Field(context->getSettingsRef().lightweight_mutation_projection_mode);
-            if (mode == "throw")
+            auto mode = context->getSettingsRef().lightweight_mutation_projection_mode;
+            if (mode == LightweightMutationProjectionMode::THROW)
             {
                 throw Exception(ErrorCodes::NOT_IMPLEMENTED,
                     "DELETE query is not supported for table {} as it has projections. "
                     "User should drop all the projections manually before running the query",
                     table->getStorageID().getFullTableName());
             }
-            else if (mode == "drop")
+            else if (mode == LightweightMutationProjectionMode::DROP)
             {
                 std::vector<String> all_projections = metadata_snapshot->projections.getAllRegisteredNames();
 

tests/queries/0_stateless/03161_lightweight_delete_projection.sql

@@ -19,6 +19,13 @@ DELETE FROM users WHERE uid = 8888 SETTINGS lightweight_mutation_projection_mode
 
 DELETE FROM users WHERE uid = 6666 SETTINGS lightweight_mutation_projection_mode = 'drop';
 
+-- expecting no projection
+SELECT
+    name,
+    `table`
+FROM system.projection_parts
+WHERE (database = currentDatabase()) AND (`table` = 'users');
+
 SELECT * FROM users;
 
 DROP TABLE users;