Started developing postgres

include/sqlgen/postgres.hpp

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+#ifndef SQLGEN_POSTGRES_HPP_
+#define SQLGEN_POSTGRES_HPP_
+
+#include "../sqlgen.hpp"
+#include "postgres/Credentials.hpp"
+#include "postgres/connect.hpp"
+
+#endif

include/sqlgen/postgres/Connection.hpp

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+#ifndef SQLGEN_POSTGRES_CONNECTION_HPP_
+#define SQLGEN_POSTGRES_CONNECTION_HPP_
+
+#include <libpq-fe.h>
+
+#include <memory>
+#include <rfl.hpp>
+#include <stdexcept>
+#include <string>
+
+#include "../Connection.hpp"
+#include "../IteratorBase.hpp"
+#include "../Ref.hpp"
+#include "../Result.hpp"
+#include "../dynamic/Column.hpp"
+#include "../dynamic/Statement.hpp"
+#include "Credentials.hpp"
+
+namespace sqlgen::postgres {
+
+class Connection : public sqlgen::Connection {
+  using ConnPtr = Ref<PGconn>;
+
+ public:
+  Connection(const Credentials& _credentials)
+      : credentials_(_credentials), conn_(make_conn(_credentials.to_str())) {}
+
+  static rfl::Result<Ref<sqlgen::Connection>> make(
+      const Credentials& _credentials) noexcept;
+
+  ~Connection() = default;
+
+  Result<Nothing> commit() final { return execute("COMMIT;"); }
+
+  Result<Nothing> execute(const std::string& _sql) noexcept final;
+
+  Result<Ref<IteratorBase>> read(const dynamic::SelectFrom& _query) final;
+
+  std::string to_sql(const dynamic::Statement& _stmt) noexcept final;
+
+  Result<Nothing> start_write(const dynamic::Insert& _stmt) final;
+
+  Result<Nothing> end_write() final;
+
+  Result<Nothing> write(
+      const std::vector<std::vector<std::optional<std::string>>>& _data) final;
+
+ private:
+  static rfl::Result<Ref<sqlgen::Connection>> make_conn(
+      const std::string& _conn_str);
+};
+
+}  // namespace sqlgen::postgres
+
+#endif

include/sqlgen/postgres/Credentials.hpp

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+#ifndef SQLGEN_POSTGRES_CREDENTIALS_HPP_
+#define SQLGEN_POSTGRES_CREDENTIALS_HPP_
+
+#include <string>
+
+namespace sqlgen::postgres {
+
+struct Credentials {
+  std::string user;
+  std::string password;
+  std::string host;
+  std::string dbname;
+  int port = 5432;
+
+  std::string to_str() const {
+    return "postgresql://" + user + ":" + password + "@" + host + ":" +
+           std::to_string(port) + "/" + dbname;
+  }
+};
+
+}  // namespace sqlgen::postgres
+
+#endif

include/sqlgen/postgres/Iterator.hpp

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+#ifndef SQLGEN_POSTGRES_ITERATOR_HPP_
+#define SQLGEN_POSTGRES_ITERATOR_HPP_
+
+#include <sqlite3.h>
+
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "../IteratorBase.hpp"
+#include "../Ref.hpp"
+#include "../Result.hpp"
+#include "Connection.hpp"
+
+namespace sqlgen::postgres {
+
+class Iterator : public sqlgen::IteratorBase {
+ public:
+  Iterator(const StmtPtr& _stmt, const ConnPtr& _conn);
+
+  ~Iterator();
+
+  /// Whether the end of the available data has been reached.
+  bool end() const final;
+
+  /// Returns the next batch of rows.
+  /// If _batch_size is greater than the number of rows left, returns all
+  /// of the rows left.
+  Result<std::vector<std::vector<std::optional<std::string>>>> next(
+      const size_t _batch_size) final;
+
+ private:
+};
+
+}  // namespace sqlgen::postgres
+
+#endif

include/sqlgen/postgres/connect.hpp

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+#ifndef SQLGEN_POSTGRES_CONNECT_HPP_
+#define SQLGEN_POSTGRES_CONNECT_HPP_
+
+#include <string>
+
+#include "Connection.hpp"
+#include "Credentials.hpp"
+
+namespace sqlgen::postgres {
+
+inline auto connect(const Credentials& _credentials) {
+  return Connection::make(_credentials);
+}
+
+}  // namespace sqlgen::postgres
+
+#endif