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alternator: add optional previous item to calculate_value

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In order to implement read-before-write in the future, calculate_value
now accepts an additional parameter: previous_item. If read-before-write
was performed, previous_item will contain an item for the given key
which already exists in the database at the time of the update.
This commit is contained in:
Piotr Sarna
2019-07-08 10:30:10 +02:00
committed by Nadav Har'El
parent 784aaaa8ff
commit 20a6077fb3
1 changed files with 12 additions and 10 deletions
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22
alternator/executor.cc
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@@ -543,7 +543,8 @@ template<class... Ts> overloaded(Ts...) -> overloaded<Ts...>;
// of other values, this function calculates the resulting value.
static Json::Value calculate_value(const parsed::value& v,
const Json::Value& expression_attribute_values,
std::unordered_set<std::string>& used_attribute_values) {
std::unordered_set<std::string>& used_attribute_values,
const std::unique_ptr<Json::Value>& previous_item) {
return std::visit(overloaded {
[&] (const std::string& valref) -> Json::Value {
const Json::Value& value = expression_attribute_values.get(valref, Json::nullValue);
@@ -560,8 +561,8 @@ static Json::Value calculate_value(const parsed::value& v,
throw api_error("ValidationException",
format("UpdateExpression: list_append() accepts 2 parameters, got {}", f._parameters.size()));
}
Json::Value v1 = calculate_value(f._parameters[0], expression_attribute_values, used_attribute_values);
Json::Value v2 = calculate_value(f._parameters[1], expression_attribute_values, used_attribute_values);
Json::Value v1 = calculate_value(f._parameters[0], expression_attribute_values, used_attribute_values, previous_item);
Json::Value v2 = calculate_value(f._parameters[1], expression_attribute_values, used_attribute_values, previous_item);
return list_concatenate(v1, v2);
} else if (f._function_name == "if_not_exists") {
// FIXME
@@ -582,18 +583,19 @@ static Json::Value calculate_value(const parsed::value& v,
// either a single value, or v1+v2 or v1-v2.
static Json::Value calculate_value(const parsed::set_rhs& rhs,
const Json::Value& expression_attribute_values,
std::unordered_set<std::string>& used_attribute_values) {
std::unordered_set<std::string>& used_attribute_values,
const std::unique_ptr<Json::Value>& previous_item) {
switch(rhs._op) {
case 'v':
return calculate_value(rhs._v1, expression_attribute_values, used_attribute_values);
return calculate_value(rhs._v1, expression_attribute_values, used_attribute_values, previous_item);
case '+': {
Json::Value v1 = calculate_value(rhs._v1, expression_attribute_values, used_attribute_values);
Json::Value v2 = calculate_value(rhs._v2, expression_attribute_values, used_attribute_values);
Json::Value v1 = calculate_value(rhs._v1, expression_attribute_values, used_attribute_values, previous_item);
Json::Value v2 = calculate_value(rhs._v2, expression_attribute_values, used_attribute_values, previous_item);
return number_add(v1, v2);
}
case '-': {
Json::Value v1 = calculate_value(rhs._v1, expression_attribute_values, used_attribute_values);
Json::Value v2 = calculate_value(rhs._v2, expression_attribute_values, used_attribute_values);
Json::Value v1 = calculate_value(rhs._v1, expression_attribute_values, used_attribute_values, previous_item);
Json::Value v2 = calculate_value(rhs._v2, expression_attribute_values, used_attribute_values, previous_item);
return number_subtract(v1, v2);
}
}
@@ -774,7 +776,7 @@ future<json::json_return_type> executor::update_item(std::string content) {
}
std::visit(overloaded {
[&] (const parsed::update_expression::action::set& a) {
auto value = calculate_value(a._rhs, update_info["ExpressionAttributeValues"], used_attribute_values);
auto value = calculate_value(a._rhs, update_info["ExpressionAttributeValues"], used_attribute_values, nullptr);
bytes val = serialize_item(value);
attrs_mut.cells.emplace_back(to_bytes(column_name), atomic_cell::make_live(*bytes_type, ts, std::move(val), atomic_cell::collection_member::yes));
},