From 5389571e2db6b62ecc8e45b5e8bea1739ab67957 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sun, 4 Jul 2021 12:48:02 +0100
Subject: Introduce the cursor concept

Not implemented for PQ yet.
---
 lib/dbConn.h                 |  1 +
 lib/dbRecordSet.h            |  8 ++++++++
 lib/input/mysqlRecordSet.cpp | 12 ++++++++++++
 lib/input/mysqlRecordSet.h   |  7 +++++++
 lib/input/mysqlStmt.cpp      |  6 ++++++
 lib/input/mysqlStmt.h        |  2 ++
 lib/output/pq/pqStmt.cpp     |  6 ++++++
 lib/output/pq/pqStmt.h       |  2 ++
 8 files changed, 44 insertions(+)

diff --git a/lib/dbConn.h b/lib/dbConn.h
index ffdd2e0..f0549d3 100644
--- a/lib/dbConn.h
+++ b/lib/dbConn.h
@@ -12,6 +12,7 @@ namespace MyGrate {
 		virtual void execute(const std::initializer_list<DbValue> &) = 0;
 		virtual std::size_t rows() const = 0;
 		virtual RecordSetPtr recordSet() = 0;
+		virtual CursorPtr cursor() = 0;
 	};
 	using DbPrepStmtPtr = std::unique_ptr<DbPrepStmt>;
 
diff --git a/lib/dbRecordSet.h b/lib/dbRecordSet.h
index a9da882..a217f12 100644
--- a/lib/dbRecordSet.h
+++ b/lib/dbRecordSet.h
@@ -49,6 +49,14 @@ namespace MyGrate {
 		RowView end() const;
 	};
 	using RecordSetPtr = std::unique_ptr<RecordSet>;
+
+	class Cursor {
+	public:
+		virtual ~Cursor() = default;
+
+		virtual bool fetch() = 0;
+	};
+	using CursorPtr = std::unique_ptr<Cursor>;
 }
 
 #endif
diff --git a/lib/input/mysqlRecordSet.cpp b/lib/input/mysqlRecordSet.cpp
index 494ce13..5fbbfe9 100644
--- a/lib/input/mysqlRecordSet.cpp
+++ b/lib/input/mysqlRecordSet.cpp
@@ -116,4 +116,16 @@ namespace MyGrate::Input {
 		}
 		return extras[col]->getValue();
 	}
+
+	bool
+	MySQLCursor::fetch()
+	{
+		switch (mysql_stmt_fetch(stmt.get())) {
+			case 0:
+				return true;
+			case MYSQL_NO_DATA:
+				return false;
+		}
+		throw MySQLErr("Fetch", stmt.get());
+	}
 }
diff --git a/lib/input/mysqlRecordSet.h b/lib/input/mysqlRecordSet.h
index d843dfd..0e3a96f 100644
--- a/lib/input/mysqlRecordSet.h
+++ b/lib/input/mysqlRecordSet.h
@@ -28,6 +28,13 @@ namespace MyGrate::Input {
 		std::vector<ResultDataPtr> extras;
 	};
 
+	class MySQLCursor : public MySQLData, public Cursor {
+	public:
+		using MySQLData::MySQLData;
+
+		bool fetch();
+	};
+
 	class MySQLRecordSet : public MySQLData, public RecordSet {
 	public:
 		using StmtResPtr = std::unique_ptr<MYSQL_STMT, decltype(&mysql_stmt_free_result)>;
diff --git a/lib/input/mysqlStmt.cpp b/lib/input/mysqlStmt.cpp
index d3ba9ef..e0f4cbc 100644
--- a/lib/input/mysqlStmt.cpp
+++ b/lib/input/mysqlStmt.cpp
@@ -33,4 +33,10 @@ namespace MyGrate::Input {
 	{
 		return std::make_unique<MySQLRecordSet>(std::move(stmt));
 	}
+
+	CursorPtr
+	MySQLPrepStmt::cursor()
+	{
+		return std::make_unique<MySQLCursor>(std::move(stmt));
+	}
 }
diff --git a/lib/input/mysqlStmt.h b/lib/input/mysqlStmt.h
index 69e62d4..09b5c73 100644
--- a/lib/input/mysqlStmt.h
+++ b/lib/input/mysqlStmt.h
@@ -23,6 +23,8 @@ namespace MyGrate::Input {
 
 		RecordSetPtr recordSet() override;
 
+		CursorPtr cursor() override;
+
 	private:
 		StmtPtr stmt;
 	};
diff --git a/lib/output/pq/pqStmt.cpp b/lib/output/pq/pqStmt.cpp
index dc258b6..2265f64 100644
--- a/lib/output/pq/pqStmt.cpp
+++ b/lib/output/pq/pqStmt.cpp
@@ -40,6 +40,12 @@ namespace MyGrate::Output::Pq {
 		return std::make_unique<PqRecordSet>(std::move(res));
 	}
 
+	CursorPtr
+	PqPrepStmt::cursor()
+	{
+		throw std::logic_error("Not implemented");
+	}
+
 	std::string
 	PqPrepStmt::prepareAsNeeded(const char * const q, std::size_t n, PqConn * c)
 	{
diff --git a/lib/output/pq/pqStmt.h b/lib/output/pq/pqStmt.h
index 6531180..887a326 100644
--- a/lib/output/pq/pqStmt.h
+++ b/lib/output/pq/pqStmt.h
@@ -27,6 +27,8 @@ namespace MyGrate::Output::Pq {
 
 		RecordSetPtr recordSet() override;
 
+		CursorPtr cursor() override;
+
 	private:
 		static std::string prepareAsNeeded(const char * const q, std::size_t n, PqConn * c);
 
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