Add get_database_product() private method to ODBC backend.

This method allows to determine what kind of database are we actually
connected to. It is private as it's not clear whether it's a good idea to
expose it (although it might, in keeping with SOCI philosophy of letting to
use the underlying database API directly if needed), but it is needed to
implement the sequence functions in the ODBC backend, so do add it.

Signed-off-by: Vadim Zeitlin <vz-soci@zeitlins.org>

src/backends/odbc/session.cpp

@@ -12,7 +12,7 @@ using namespace soci;
 using namespace soci::details;
 
 odbc_session_backend::odbc_session_backend(std::string const & connectString)
-    : henv_(0), hdbc_(0)
+    : henv_(0), hdbc_(0), product_(prod_uninitialized)
 {
     SQLRETURN rc;
 
@@ -145,3 +145,37 @@ odbc_blob_backend * odbc_session_backend::make_blob_backend()
 {
     return new odbc_blob_backend(*this);
 }
+
+odbc_session_backend::database_product
+odbc_session_backend::get_database_product()
+{
+    // Cache the product type, it's not going to change during our life time.
+    if (product_ != prod_uninitialized)
+        return product_;
+
+    char product_name[1024];
+    SQLSMALLINT len = sizeof(product_name);
+    SQLRETURN rc = SQLGetInfo(hdbc_, SQL_DBMS_NAME, product_name, len, &len);
+    if (is_odbc_error(rc))
+    {
+        throw odbc_soci_error(SQL_HANDLE_DBC, henv_,
+                            "SQLGetInfo(SQL_DBMS_NAME)");
+    }
+
+    if (strcmp(product_name, "Firebird") == 0)
+        product_ = prod_firebird;
+    else if (strcmp(product_name, "Microsoft SQL Server") == 0)
+        product_ = prod_mssql;
+    else if (strcmp(product_name, "MySQL") == 0)
+        product_ = prod_mysql;
+    else if (strcmp(product_name, "Oracle") == 0)
+        product_ = prod_oracle;
+    else if (strcmp(product_name, "PostgreSQL") == 0)
+        product_ = prod_postgresql;
+    else if (strcmp(product_name, "SQLite") == 0)
+        product_ = prod_sqlite;
+    else
+        product_ = prod_unknown;
+
+    return product_;
+}

src/backends/odbc/soci-odbc.h

@@ -253,8 +253,26 @@ struct odbc_session_backend : details::session_backend
     virtual odbc_rowid_backend * make_rowid_backend();
     virtual odbc_blob_backend * make_blob_backend();
 
+    enum database_product
+    {
+      prod_uninitialized, // Never returned by get_database_product().
+      prod_firebird,
+      prod_mssql,
+      prod_mysql,
+      prod_oracle,
+      prod_postgresql,
+      prod_sqlite,
+      prod_unknown = -1
+    };
+
+    // Determine the type of the database we're connected to.
+    database_product get_database_product();
+
+
     SQLHENV henv_;
     SQLHDBC hdbc_;
+
+    database_product product_;
 };
 
 class SOCI_ODBC_DECL odbc_soci_error : public soci_error