#118 add support for LIMIT & OFFSET

Author: SingingBush

.github/workflows/dub.yml

@@ -19,26 +19,32 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-latest, windows-latest, macos-latest ]
+        os: [ ubuntu-latest, windows-latest ]
         compiler:
           - dmd-latest
           - ldc-latest
-          - dmd-2.102.2
-          - dmd-2.101.2
-          - dmd-2.100.2
-          - dmd-2.099.1
-          - dmd-2.098.1
-          - dmd-2.097.2
+          - dmd-2.103.1 # (released in 2023)
+          - dmd-2.102.2 # (released in 2023)
+          - dmd-2.101.2 # (released in 2023)
+          - dmd-2.100.2 # (released in 2022) ## GDC 12 can support 2.100
+          - dmd-2.099.1 # (released in 2022)
+          - dmd-2.098.1 # (released in 2021) ## Has issue re: phobos/std/variant.d
+          - dmd-2.097.2 # (released in 2021)
+          - ldc-1.33.0 # eq to dmd v2.103.1
+          - ldc-1.32.2 # eq to dmd v2.102.2
           - ldc-1.28.1 # eq to dmd v2.098.1
           - ldc-1.27.1 # eq to dmd v2.097.2
+        include:
+          - { os: macos-latest, compiler: dmd-latest }
+          - { os: macos-latest, compiler: ldc-latest }
+          - { os: macos-latest, compiler: dmd-2.100.2 }
+          - { os: macos-latest, compiler: ldc-1.32.2 }
         exclude:
           - { os: windows-latest, compiler: dmd-2.098.1 }
           - { os: windows-latest, compiler: dmd-2.097.2 }
-          - { os: macos-latest, compiler: dmd-2.098.1 }
-          - { os: macos-latest, compiler: dmd-2.097.2 }
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install D ${{ matrix.compiler }}
         uses: dlang-community/setup-dlang@v1

README.md

@@ -102,6 +102,11 @@ foreach(ref e; stmt.select!User.where("id < 6").orderBy("name desc")) {
     writeln("id:", e.id, " name:", e.name, " flags:", e.flags);
 }
 
+writeln("reading user table rows with where and order by with limit and offset");
+foreach(e; stmt.select!User.where("id < 6").orderBy("name desc").limit(3).offset(1)) {
+    writeln("id:", e.id, " name:", e.name, " flags:", e.flags);
+}
+
 writeln("reading all user table rows, but fetching only id and name (you will see default value 0 in flags field)");
 foreach(ref e; stmt.select!(User, "id", "name")) {
     writeln("id:", e.id, " name:", e.name, " flags:", e.flags);

docker-compose.yml

@@ -7,6 +7,10 @@ services:
     #image: mariadb:latest
     restart: always
     ports: ['3306:3306', '33060:33060']
+    ulimits:
+      nofile:
+        soft: "1024"
+        hard: "10240"
     environment:
       - MYSQL_ROOT_PASSWORD=f48dfhw3Hd!Asah7i2aZ
       - MYSQL_DATABASE=testdb

example/dub.json

@@ -6,7 +6,7 @@
     "license": "Boost Software License (BSL 1.0)",
     "dependencies": {
         "ddbc": {"version": "~master", "path": "../"},
-        "vibe-d": "~>0.9.4"
+        "vibe-core": "1.22.6"
     },
     "targetType": "executable",
     "buildRequirements": [

example/source/testddbc.d

@@ -149,6 +149,8 @@ int main(string[] args)
 				}
 				version( USE_SQLITE ) {
 					driver = new SQLITEDriver();
+					//url = chompPrefix(URI, "sqlite:");
+					//url = SQLITEDriver.generateUrl();
 				}
 				url = chompPrefix(URI, "sqlite:");
 				break;
@@ -368,7 +370,7 @@ int main(string[] args)
     int i = 0;
 
     while (rs.next()) {
-        writeln("\tid: " ~ to!string(rs.getLong(1)) ~ "\t" ~ rs.getString(2));
+        writeln(" - id: " ~ to!string(rs.getLong(1)) ~ "\t" ~ rs.getString(2));
         i++;
     }
 	writefln("\tThere were %,d rows returned from the ddbct1 table...", i);
@@ -383,7 +385,7 @@ int main(string[] args)
     rs = stmt.executeQuery("SELECT id,comment FROM ddbct1 WHERE id = 2");
     i = 0;
     while (rs.next()) {
-        writeln("\tid: " ~ to!string(rs.getLong(1)) ~ "\t" ~ rs.getString(2));
+        writeln(" - id: " ~ to!string(rs.getLong(1)) ~ "\t" ~ rs.getString(2));
         i++;
     }
     assert(1 == i, "There should be 1 result but instead there was " ~ to!string(i));
@@ -392,7 +394,7 @@ int main(string[] args)
 	i = 0;
 	rs = stmt.executeQuery("SELECT id, comment, ts FROM ddbct1 ORDER BY id DESC");
 	while (rs.next()) {
-		writeln("\tid: " ~ to!string(rs.getLong(1)) ~ "\t" ~ rs.getString(2) ~ "\t" ~ to!string(rs.getDateTime(3)));
+		writeln(" - id: " ~ to!string(rs.getLong(1)) ~ "\t" ~ rs.getString(2) ~ "\t" ~ to!string(rs.getDateTime(3)));
 		i++;
 	}
 	assert(2 == i, "There should be 2 results but instead there was " ~ to!string(i));
@@ -410,7 +412,7 @@ int main(string[] args)
 		assert(rs.getDateTime(4).month == dtNow.month);
 		assert(rs.getDateTime(4).day == dtNow.day);
 		assert(rs.getDateTime(4).hour == dtNow.hour);
-		writeln("\tid: " ~ to!string(rs.getLong(1)) ~ "\t" ~ rs.getString(2) ~ "\t" ~ to!string(rs.getDateTime(4)));
+		writeln(" - id: " ~ to!string(rs.getLong(1)) ~ "\t" ~ rs.getString(2) ~ "\t" ~ to!string(rs.getDateTime(4)));
 
 		// ddbc should also allow you to retrive the timestamp as a SysTime (defaulting UTC if no zone info given)
 		assert(rs.getSysTime(4).year == now.year);
@@ -420,14 +422,19 @@ int main(string[] args)
 		i++;
 	}
 	assert(2 == i, "There should be 2 results but instead there was " ~ to!string(i));
+	if(par.driver != "odbc") {
+		// ODBC doesn't support ResultSet::getFetchSize()
+		ulong fetchSize = rs.getFetchSize();
+		assert(i == fetchSize, "ResultSet::getFetchSize() should have returned " ~ to!string(i) ~ " but was " ~ to!string(fetchSize));
+	}
 
     writeln("\n > Testing prepared SQL statements");
 	PreparedStatement ps2 = conn.prepareStatement("SELECT id, name name_alias, comment, ts FROM ddbct1 WHERE id >= ?");
     scope(exit) ps2.close();
     ps2.setUlong(1, 1);
     auto prs = ps2.executeQuery();
     while (prs.next()) {
-        writeln("\tid: " ~ to!string(prs.getLong(1)) ~ "\t" ~ prs.getString(2) ~ "\t" ~ prs.getString(3) ~ "\t" ~ to!string(prs.getDateTime(4)));
+        writeln(" - id: " ~ to!string(prs.getLong(1)) ~ "\t" ~ prs.getString(2) ~ "\t" ~ prs.getString(3) ~ "\t" ~ to!string(prs.getDateTime(4)));
     }
 
 	writeln("\n > Testing basic POD support");
@@ -442,26 +449,51 @@ int main(string[] args)
         SysTime updated;
     }
 
-	immutable SysTime now = Clock.currTime();
+	immutable DateTime now = cast(DateTime) Clock.currTime();
 
 	writeln(" > select all rows from employee table");
     foreach(ref e; conn.createStatement().select!Employee) {
 		//SysTime nextMonth = now.add!"months"(1);
 
-        writeln("\t{id: ", e.id, ", name: ", e.name, ", flags: ", e.flags, ", dob: ", e.dob, ", created: ", e.created, ", updated: ", e.updated, "}");
+        writeln(" - {id: ", e.id, ", name: ", e.name, ", flags: ", e.flags, ", dob: ", e.dob, ", created: ", e.created, ", updated: ", e.updated, "}");
 		assert(e.name !is null);
 		assert(e.dob.year > 1950);
-		assert(e.created <= cast(DateTime) now);
-		assert(e.updated <= now);
-    }
+		assert(e.created <= now);
+		assert(cast(DateTime) e.updated <= now, "Updated '" ~ to!string(e.updated) ~ "' should be <= '" ~ to!string(now) ~ "'");
+	}
 
+	i = 0;
     writeln(" > select all rows from employee table WHERE id < 4 ORDER BY name DESC...");
     foreach(ref e; conn.createStatement().select!Employee.where("id < 4").orderBy("name desc")) {
-        writeln("\t{id: ", e.id, ", name: ", e.name, ", flags: ", e.flags, ", dob: ", e.dob, ", created: ", e.created, ", updated: ", e.updated, "}");
+        writeln(" - {id: ", e.id, ", name: ", e.name, ", flags: ", e.flags, ", dob: ", e.dob, ", created: ", e.created, ", updated: ", e.updated, "}");
 		assert(e.id < 4);
 		assert(e.name != "Iain" && e.name != "Robert");
 		assert(e.flags > 1);
+		i++;
     }
+	assert(3 == i, "There should be 3 results but instead there was " ~ to!string(i));
+
+	i = 0;
+	writeln(" > select all rows from employee table WHERE id < 4 LIMIT 2...");
+    foreach(ref e; conn.createStatement().select!Employee.where("id < 4").orderBy("id ASC").limit(2)) {
+        writeln(" - {id: ", e.id, ", name: ", e.name, ", flags: ", e.flags, ", dob: ", e.dob, ", created: ", e.created, ", updated: ", e.updated, "}");
+		assert(e.id == 1 || e.id == 2, "results should start from id 1 as there's no offset");
+		assert(e.name != "Iain" && e.name != "Robert");
+		assert(e.flags > 1);
+		i++;
+    }
+	assert(2 == i, "There should be 2 results but instead there was " ~ to!string(i));
+
+	i = 0;
+	writeln(" > select all rows from employee table WHERE id < 4 LIMIT 2 OFFSET 1...");
+    foreach(ref e; conn.createStatement().select!Employee.where("id < 4").orderBy("id ASC").limit(2).offset(1)) {
+        writeln(" - {id: ", e.id, ", name: ", e.name, ", flags: ", e.flags, ", dob: ", e.dob, ", created: ", e.created, ", updated: ", e.updated, "}");
+		assert(e.id == 2 || e.id == 3, "results should start from id 2 due to offset");
+		assert(e.name != "Iain" && e.name != "Robert");
+		assert(e.flags > 1);
+		i++;
+    }
+	assert(2 == i, "There should be 2 results but instead there was " ~ to!string(i));
 
 	// todo: Fix the UPDATE/INSERT functionality for PODs
 	// Employee e; 

source/ddbc/common.d

@@ -94,6 +94,12 @@ class ConnectionWrapper : Connection {
 		this.pool = pool;
 		this.base = base;
 	}
+
+	// a db connection is DialectAware
+	override Dialect getDialect() {
+		return base.getDialect();
+	}
+
 	override void close() {
 		assert(!closed, "Connection is already closed");
 		closed = true;
@@ -234,7 +240,7 @@ public:
             result = dg(cast(DataSetReader)this); 
             if (result) break; 
         } while (next());
-        return result; 
+        return result;
     }
     override void close() {
 		throw new SQLException("Method not implemented");
@@ -248,6 +254,7 @@ public:
 	override bool isLast() {
 		throw new SQLException("Method not implemented");
 	}
+	/// returns true if ResultSet object contains more rows
 	override bool next() {
 		throw new SQLException("Method not implemented");
 	}

source/ddbc/core.d

@@ -134,7 +134,7 @@ enum SqlType {
 	VARCHAR,
 }
 
-interface Connection {
+interface Connection : DialectAware {
 	/// Releases this Connection object's database and JDBC resources immediately instead of waiting for them to be automatically released.
 	void close();
 	/// Makes all changes made since the previous commit/rollback permanent and releases any database locks currently held by this Connection object.
@@ -342,7 +342,21 @@ interface ResultSet : DataSetReader {
 
 }
 
-interface Statement {
+enum Dialect {
+	SQLITE, // SQLite has it's own quirks
+	MYSQL5, // for MySQL & MariaDB
+	MYSQL8, // todo: add support for MySQL 8
+	PGSQL, // PL/pgSQL (Procedural Language/PostgreSQL) used by PostgreSQL
+	TSQL, // T-SQL (Transact-SQL) is Microsoft’s extension of SQL
+	PLSQL // Oracle (PL/SQL)
+}
+
+interface DialectAware {
+	Dialect getDialect();
+}
+
+// statements are made via a db connection which are also DialectAware
+interface Statement : DialectAware {
 	ResultSet executeQuery(string query);
 	int executeUpdate(string query);
 	int executeUpdate(string query, out Variant insertId);

source/ddbc/drivers/mysqlddbc.d

@@ -119,6 +119,11 @@ private:
 
 public:
 
+    // db connections are DialectAware
+    override Dialect getDialect() {
+        return Dialect.MYSQL5; // TODO: add support for MySQL8
+    }
+
     void lock() {
         mutex.lock();
     }
@@ -306,6 +311,11 @@ private:
     bool closed;
 
 public:
+    // statements are DialectAware
+    override Dialect getDialect() {
+        return conn.getDialect();
+    }
+
     void checkClosed() {
         enforce!SQLException(!closed, "Statement is already closed");
     }
@@ -447,6 +457,11 @@ class MySQLPreparedStatement : MySQLStatement, PreparedStatement {
     }
 public:
 
+    // prepared statements are DialectAware
+    override Dialect getDialect() {
+        return conn.getDialect();
+    }
+
     /// Retrieves a ResultSetMetaData object that contains information about the columns of the ResultSet object that will be returned when this PreparedStatement object is executed.
     override ResultSetMetaData getMetaData() {
         checkClosed();

source/ddbc/drivers/odbcddbc.d

@@ -336,21 +336,23 @@ version (USE_ODBC)
             }
         }
 
-        void checkClosed()
-        {
+        void checkClosed() {
             if (closed)
                 throw new SQLException("Connection is already closed");
         }
 
     public:
 
-        void lock()
-        {
+        // db connections are DialectAware
+        override Dialect getDialect() {
+            return Dialect.TSQL; // todo: handle TSQL and PLSQL
+        }
+
+        void lock() {
             mutex.lock();
         }
 
-        void unlock()
-        {
+        void unlock() {
             mutex.unlock();
         }
 
@@ -582,14 +584,17 @@ version (USE_ODBC)
         bool closed = false;
 
         private SQLRETURN checkstmt(alias Fn, string file = __FILE__, size_t line = __LINE__)(
-                Parameters!Fn args)
-        {
+                Parameters!Fn args) {
             return check!(Fn, file, line)(stmt, SQL_HANDLE_STMT, args);
         }
 
     public:
-        void checkClosed()
-        {
+        // statements are DialectAware
+        override Dialect getDialect() {
+            return conn.getDialect();
+        }
+
+        void checkClosed() {
             enforce!SQLException(!closed, "Statement is already closed");
         }
 
@@ -988,6 +993,11 @@ version (USE_ODBC)
 
     public:
 
+        // prepared statements are DialectAware
+        override Dialect getDialect() {
+            return conn.getDialect();
+        }
+
         /// Retrieves a ResultSetMetaData object that contains information about the columns of the ResultSet object that will be returned when this PreparedStatement object is executed.
         override ResultSetMetaData getMetaData()
         {