Hi together,
first of all, thanks for soci, it's great stuff and eases our database
tasks quite a lot.
Recently, we have implemented a type conversion for our variant class,
which enables us to store even multi-hierarchical data into a soci
connection.
To give an example:
void masterclient(soci::session &sql) {
variant master;
master["cost"] = 1234.56f;
master["name"] = "test";
master["details"] = 2;
for (size_t i = 0; i < master["details"].asSize(); ++i) {
variant detail;
detail["master_idx"] = "%PARENT%";
detail["id"] = i;
detail["data"] = "xyz";
master["{details}"].push_back(std::move(detail));
};
vdb::storeTables(sql, "master", master);
}
Remarks:
%PARENT% is a placeholder for the last_insert_id, which maps the
relationship between master and detail here
{}-field names indicate sub-table objects to avoid name clashes with the
same name
Instead of using variant classes here, we could of course use any
tree-like data structure, like xml.
Whatever... in the end, we have to convert the variant (the data) to
something that soci understands. So we have implemented the
type_conversion specialization:
namespace soci {
template<> struct type_conversion<variant> {
typedef values base_type;
static void from_base(values const &v, indicator ind, variant &out) {
...
At this point, we have to map fields from 'values' into our variant
'out'. However, there's no way in iterating the values here, nor is
there a way to figure out the size of values. Ouch.
To enable our implementation, we have changed values.h around line 221:
+ inline row * GetRow() const {
+ return row_;
+ }
This enables us (somehow) to iterate the values, and retrieve type
information for each row:
soci::row *row = v.GetRow();
for (size_t x = 0; x < row->size(); ++x) {
const column_properties &props = v.get_properties(x);
const char *colname = props.get_name().c_str();
if (v.get_indicator(x) == i_null) {
out[colname] = nullptr;
} else {
switch (props.get_data_type()) {
case dt_string:
// store into variant as string
...
However, I have no evidence that the row and the values are 'the same
thing', and I don't feel to happy about this solution. Now here's my
question: could you guys provide an iterator for the values class, or
expose (e.g. a const row) accessor inside values?
Or is there any other method you recommand to get this particular job done?
Any hints appreciated!
Thanks and cheers,
Roman
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