Added Block::Clear() and some tests

Author: Enmk

clickhouse/block.cpp

@@ -81,8 +81,7 @@ size_t Block::GetRowCount() const {
     return rows_;
 }
 
-size_t Block::RefreshRowCount()
-{
+size_t Block::RefreshRowCount() {
     size_t rows = 0UL;
 
     for (size_t idx = 0UL; idx < columns_.size(); ++idx)
@@ -100,6 +99,15 @@ size_t Block::RefreshRowCount()
     return rows_;
 }
 
+void Block::Clear() {
+    for (auto & c : columns_) {
+        c.column->Clear();
+    }
+
+    RefreshRowCount();
+}
+
+
 ColumnRef Block::operator [] (size_t idx) const {
     if (idx < columns_.size()) {
         return columns_[idx].column;

clickhouse/block.h

@@ -85,6 +85,9 @@ class Block {
         return columns_.at(idx).name;
     }
 
+    /// Convinience method to wipe out all rows from all columns
+    void Clear();
+
     /// Reference to column by index in the block.
     ColumnRef operator [] (size_t idx) const;
 

ut/block_ut.cpp

@@ -1,4 +1,9 @@
 #include <clickhouse/client.h>
+#include <clickhouse/columns/tuple.h>
+#include <clickhouse/types/types.h>
+
+#include "clickhouse/columns/column.h"
+#include "gtest/gtest-message.h"
 #include "readonly_client_test.h"
 #include "connection_failed_client_test.h"
 #include "utils.h"
@@ -83,3 +88,43 @@ TEST(BlockTest, Iterators) {
     ASSERT_NE(block.cbegin(), block.cend());
 }
 
+TEST(BlockTest, Clear) {
+    // Test that Block::Clear removes all rows from all of the columns,
+    // without changing column instances, types, names, etc.
+
+    auto block = MakeBlock({
+        {"foo", std::make_shared<ColumnUInt8>(std::vector<uint8_t>{1, 2, 3, 4, 5})},
+        {"bar", std::make_shared<ColumnString>(std::vector<std::string>{"1", "2", "3", "4", "5"})},
+    });
+
+    std::vector<std::tuple<std::string, Column*>> expected_columns_description;
+    for (const auto & c : block) {
+        expected_columns_description.emplace_back(c.Name(), c.Column().get());
+    }
+
+    block.Clear();
+
+    // Block must report empty after being cleared
+    EXPECT_EQ(0u, block.GetRowCount());
+
+    size_t i = 0;
+    for (const auto & c : block) {
+        const auto & [expected_name, expected_column] = expected_columns_description[i];
+        SCOPED_TRACE(testing::Message("col #") << c.ColumnIndex() << " \"" << c.Name() << "\"");
+
+        // MUST be same column object
+        EXPECT_EQ(expected_column, c.Column().get());
+
+        // MUST have same column name
+        EXPECT_EQ(expected_name, c.Name());
+
+        // column MUST be empty
+        EXPECT_EQ(0u, c.Column()->Size())
+            << c.ColumnIndex() << " : " << c.Name();
+
+        ++i;
+        EXPECT_FALSE(true);
+    }
+}
+
+