initial

Author: ajermakovics

.gitignore

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+.gradle/ 
+.classpath 
+.project 
+.settings/
+*.class
+*.jar
+bin/
+build/
+target/
+

build.gradle

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+apply plugin: 'java'
+apply plugin: 'eclipse'
+
+sourceCompatibility = 1.8
+targetCompatibility = 1.8
+
+version = '0.1'
+jar {
+    manifest {
+        attributes 'Implementation-Title': 'Lambda2sql', 'Implementation-Version': version
+    }
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    compile 'com.trigersoft:jaque:2.0.4'
+
+    testCompile group: 'junit', name: 'junit', version: '4.+'
+}
+
+test {
+    systemProperties 'jdk.internal.lambda.dumpProxyClasses': '/tmp'
+}
+
+uploadArchives {
+    repositories {
+       flatDir {
+           dirs 'repos'
+       }
+    }
+}

src/main/java/lambda2sql/Lambda2Sql.java

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+package lambda2sql;
+
+import static java.nio.file.Files.createTempDirectory;
+
+import java.io.IOException;
+import java.util.function.Predicate;
+
+import com.trigersoft.jaque.expression.LambdaExpression;
+
+/**
+ * A utility class for converting java lambdas to SQL.
+ * It must be initializes with {@link #init()} before any lambdas are created.
+ */
+public class Lambda2Sql {
+
+	private static final String DUMP_CLASSES_PROP = "jdk.internal.lambda.dumpProxyClasses";
+
+	/**
+	 * Initializes the jdk.internal.lambda.dumpProxyClasses system property with a temporary directory.
+	 * See https://bugs.openjdk.java.net/browse/JDK-8023524
+	 */
+	public static void init() {
+		try {
+			if( System.getProperty(DUMP_CLASSES_PROP) == null )
+				System.setProperty(DUMP_CLASSES_PROP, createTempDirectory("lambda").toString());
+		} catch (IOException e) {
+			throw new IllegalStateException(e);
+		}
+	}
+
+	/**
+	 * Converts a predicate lambda to SQL. Make sure to {@link Lamda2Sql#init()} before creating the predicate.<br/>
+	 * <pre>{@code person -> person.getAge() > 50 && person.isActive() }</pre>
+	 * Becomes a string:
+	 * <pre>{@code "age > 50 AND active" }</pre>
+	 * Supported operators: >,>=,<,<=,=,!=,&&,||,!
+	 */
+	public static <T> String toSql(Predicate<T> predicate) {
+		LambdaExpression<Predicate<T>> lambdaExpression = LambdaExpression.parse(predicate);
+		return lambdaExpression.accept(new ToSqlVisitor());
+	}
+}

src/main/java/lambda2sql/ToSqlVisitor.java

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+package lambda2sql;
+
+import static com.trigersoft.jaque.expression.ExpressionType.Equal;
+import static com.trigersoft.jaque.expression.ExpressionType.LogicalAnd;
+import static com.trigersoft.jaque.expression.ExpressionType.LogicalOr;
+
+import com.trigersoft.jaque.expression.*;
+
+public class ToSqlVisitor implements ExpressionVisitor<String> {
+
+	boolean top = true;
+
+
+	@Override
+	public String visit(BinaryExpression e) {
+		boolean quote = !top && e.getExpressionType() == LogicalOr;
+		top = false;
+
+		StringBuilder sb = new StringBuilder();
+		if( quote ) sb.append('(');
+
+		String first = e.getFirst().accept(this);
+		String second = e.getSecond().accept(this);
+
+		sb.append(first).append(' ').append(toSqlOp(e.getExpressionType())).append(' ').append(second);
+
+		if( quote ) sb.append(')');
+
+		return sb.toString();
+	}
+
+	public static String toSqlOp(int expressionType) {
+		switch(expressionType) {
+			case Equal: return "=";
+			case LogicalAnd: return "AND";
+			case LogicalOr: return "OR";
+		}
+		return ExpressionType.toString(expressionType);
+	}
+
+	@Override
+	public String visit(ConstantExpression e) {
+		return e.getValue().toString();
+	}
+
+	@Override
+	public String visit(InvocationExpression e) {
+		return e.getTarget().accept(this);
+	}
+
+	@Override
+	public String visit(LambdaExpression<?> e) {
+		return e.getBody().accept(this);
+	}
+
+	@Override
+	public String visit(MemberExpression e) {
+		String name = e.getMember().getName();
+		return name.replaceAll("^(get|is)", "").toLowerCase();
+	}
+
+	@Override
+	public String visit(ParameterExpression e) {
+		return "";
+	}
+
+	@Override
+	public String visit(UnaryExpression e) {
+		String first = e.getFirst().accept(this);
+		return ExpressionType.toString(e.getExpressionType()) + first;
+	}
+
+}

src/test/java/lambda2sql/Lambda2SqlTest.java

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+package lambda2sql;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.function.Predicate;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+
+public class Lambda2SqlTest {
+
+	@BeforeClass
+	public static void init() throws Exception {
+		Lambda2Sql.init();
+	}
+
+	@Test
+	public void testComparisons() throws Exception {
+		assertEqual("age = 1", e -> e.getAge() == 1);
+		assertEqual("age > 1", e -> e.getAge() > 1);
+		assertEqual("age < 1", e -> e.getAge() < 1);
+		assertEqual("age >= 1", e -> e.getAge() >= 1);
+		assertEqual("age <= 1", e -> e.getAge() <= 1);
+		assertEqual("age != 1", e -> e.getAge() != 1);
+	}
+
+	@Test
+	public void testLogicalOps() throws Exception {
+		assertEqual("!active", e -> ! e.isActive() );
+		assertEqual("age < 100 AND height > 200", e -> e.getAge() < 100 && e.getHeight() > 200 );
+		assertEqual("age < 100 OR height > 200", e -> e.getAge() < 100 || e.getHeight() > 200 );
+	}
+
+	@Test
+	public void testMultiLogicalOps() throws Exception {
+		assertEqual("active AND (age < 100 OR height > 200)", e -> e.isActive() && (e.getAge() < 100 || e.getHeight() > 200) );
+	}
+
+	private void assertEqual(String expectedSql, Predicate<Person> p) {
+		String sql = Lambda2Sql.toSql(p);
+		assertEquals(expectedSql, sql);
+	}
+}

src/test/java/lambda2sql/Person.java

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+package lambda2sql;
+
+public interface Person {
+
+	public String getName();
+	public int getAge();
+	public int getHeight();
+	public boolean isActive();
+
+}