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alternator: add set difference helper function

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A function for computing set differene of two sets represented
as JSON is added.
This commit is contained in:
Piotr Sarna
2019-07-12 12:44:13 +02:00
committed by Nadav Har'El
parent 493890c6f6
commit 1d19934bc6
1 changed files with 23 additions and 0 deletions
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23
alternator/executor.cc
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@@ -580,6 +580,29 @@ static Json::Value set_sum(const Json::Value& v1, const Json::Value& v2) {
return ret;
}
// Take two JSON-encoded set values (e.g. {"SS": [...the actual list]}) and return the difference of s1 - s2,
// again as a set value.
static Json::Value set_diff(const Json::Value& v1, const Json::Value& v2) {
auto [set1_type, set1] = unwrap_set(v1);
auto [set2_type, set2] = unwrap_set(v2);
if (set1_type != set2_type) {
throw api_error("ValidationException", format("Mismatched set types: {} and {}", set1_type, set2_type));
}
if (!set1 || !set2) {
throw api_error("ValidationException", "UpdateExpression: DELETE operation can only be performed on a set");
}
std::set<Json::Value> set1_raw(set1->begin(), set1->end());
for (const auto& a : *set2) {
set1_raw.erase(a);
}
Json::Value ret(Json::objectValue);
Json::Value& result_set = ret[set1_type];
for (const auto& a : set1_raw) {
result_set.append(a);
}
return ret;
}
// Check if a given JSON object encodes a number (i.e., it is a {"N": [...]}
// and returns an object representing it.
static big_decimal unwrap_number(const Json::Value& v) {