add methods for checking existence on table assertion

part for resolving #12

Author: Avinash-Bhat

src/main/java/org/assertj/db/api/AbstractDbAssert.java

@@ -49,7 +49,7 @@ public abstract class AbstractDbAssert<D extends AbstractDbData<D>, A extends Ab
   /**
    * The actual value on which the assertion is.
    */
-  private final D actual;
+  protected final D actual;
 
   /**
    * Position of navigation to column.

src/main/java/org/assertj/db/api/TableAssert.java

@@ -12,6 +12,8 @@
  */
 package org.assertj.db.api;
 
+import org.assertj.db.api.assertions.AssertOnExistence;
+import org.assertj.db.api.assertions.impl.AssertionsOnTableExistence;
 import org.assertj.db.type.Table;
 
 /**
@@ -21,7 +23,8 @@
  * 
  */
 public class TableAssert
-        extends AbstractDbAssert<Table, TableAssert, TableColumnAssert, TableColumnValueAssert, TableRowAssert, TableRowValueAssert> {
+        extends AbstractDbAssert<Table, TableAssert, TableColumnAssert, TableColumnValueAssert, TableRowAssert, TableRowValueAssert>
+        implements AssertOnExistence<TableAssert> {
 
   /**
    * Constructor.
@@ -31,4 +34,38 @@ public class TableAssert
   TableAssert(Table table) {
     super(table, TableAssert.class, TableColumnAssert.class, TableRowAssert.class);
   }
+
+  /**
+   * Verifies that the table exist.
+   * <p>
+   * Example where the assertion verifies that the table exists:
+   * </p>
+   *
+   * <pre><code class='java'>
+   * assertThat(table).exists();
+   * </code></pre>
+   *
+   * @return {@code this} assertion object.
+   */
+  @Override
+  public TableAssert exists() {
+    return AssertionsOnTableExistence.exists(this, info, actual.getName(), actual.getSource(), actual.getDataSource());
+  }
+
+  /**
+   * Verifies that the table doesn't exist.
+   * <p>
+   * Example where the assertion verifies that the table doesn't exists:
+   * </p>
+   *
+   * <pre><code class='java'>
+   * assertThat(table).doesNotExists();
+   * </code></pre>
+   *
+   * @return {@code this} assertion object.
+   */
+  @Override
+  public TableAssert doesNotExist() {
+    return null;
+  }
 }

src/main/java/org/assertj/db/api/assertions/AssertOnExistence.java

@@ -0,0 +1,26 @@
+package org.assertj.db.api.assertions;
+
+/**
+ * Defines the assertion method on existence of something.
+ *
+ * @param <T> The "self" type of this assertion class. Please read &quot;<a href="http://bit.ly/1IZIRcY"
+ *            target="_blank">Emulating 'self types' using Java Generics to simplify fluent API implementation</a>&quot;
+ *            for more details.
+ * @author Avinash Ananth Narayan R
+ */
+public interface AssertOnExistence<T extends AssertOnExistence<T>> {
+
+  /**
+   * Verifies that the thing represented exist.
+   *
+   * @return {@code this} assertion object.
+   */
+  T exists();
+
+  /**
+   * Verifies that the thing represented doesn't exist.
+   *
+   * @return {@code this} assertion object.
+   */
+  T doesNotExist();
+}

src/main/java/org/assertj/db/api/assertions/AssertOnRowOfChangeExistence.java

@@ -20,7 +20,8 @@
  *            for more details.
  * @author Régis Pouiller
  */
-public interface AssertOnRowOfChangeExistence<T extends AssertOnRowOfChangeExistence<T>> {
+public interface AssertOnRowOfChangeExistence<T extends AssertOnRowOfChangeExistence<T>> extends
+    AssertOnExistence<T> {
 
   /**
    * Verifies that the row of the change exists.

src/main/java/org/assertj/db/api/assertions/impl/AssertionsOnTableExistence.java

@@ -0,0 +1,74 @@
+package org.assertj.db.api.assertions.impl;
+
+import org.assertj.core.api.WritableAssertionInfo;
+import org.assertj.core.internal.Failures;
+import org.assertj.db.api.AbstractDbAssert;
+import org.assertj.db.exception.AssertJDBException;
+import org.assertj.db.type.Source;
+
+import java.sql.Connection;
+import java.sql.DatabaseMetaData;
+import java.sql.DriverManager;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+
+import javax.sql.DataSource;
+
+import static org.assertj.db.error.ShouldExist.shouldExist;
+import static org.assertj.db.error.ShouldNotExist.shouldNotExist;
+
+/**
+ * Implements the assertion method on the existence of a table
+ * @author Avinash Ananth Narayan
+ */
+public class AssertionsOnTableExistence {
+
+  /**
+   * To notice failures in the assertion.
+   */
+  private final static Failures failures = Failures.instance();
+
+  private AssertionsOnTableExistence() {
+    // Empty
+  }
+
+  public static <A extends AbstractDbAssert> A exists(A assertion, WritableAssertionInfo info,
+                                                      String table, Source source, DataSource dataSource) {
+    try (Connection connection = getConnection(source, dataSource)) {
+      DatabaseMetaData metaData = connection.getMetaData();
+      ResultSet result = metaData.getTables(null, null, table, null);
+      if (!result.next()) {
+        throw failures.failure(info, shouldExist());
+      }
+      result.close();
+    } catch (SQLException e) {
+      throw new AssertJDBException(e);
+    }
+    return assertion;
+  }
+
+  public static <A extends AbstractDbAssert> A doesNotExists(A assertion, WritableAssertionInfo info,
+                                                             String table, Source source, DataSource dataSource) {
+    try (Connection connection = getConnection(source, dataSource)) {
+      DatabaseMetaData metaData = connection.getMetaData();
+      ResultSet result = metaData.getTables(null, null, table, null);
+      if (result.next()) {
+        throw failures.failure(info, shouldNotExist());
+      }
+      result.close();
+    } catch (SQLException e) {
+      throw new AssertJDBException(e);
+    }
+    return assertion;
+  }
+
+  private static Connection getConnection(Source source, DataSource dataSource) throws SQLException {
+    if (source == null && dataSource == null) {
+      throw new NullPointerException("connection or dataSource must be not null");
+    }
+    if (dataSource != null) {
+      return dataSource.getConnection();
+    }
+    return DriverManager.getConnection(source.getUrl(), source.getUser(), source.getPassword());
+  }
+}