Feature/ddl migration (#1111)

* REFACTOR: use functions from ddl-help

* NEW: Default values are written to DDL

* fix testcase for sqlserver as default constraints will get names in future

* Reading DbMigration

* ADD: DbmIgrationGenerateTest

* Tables must be created first

* Sanity checks and some getters

* DdlMigration gets applied now

* ADD: Testcase and reference migration scripts

* no effective code changes: add comments

src/main/java/io/ebeaninternal/server/deploy/DbMigrationInfo.java

@@ -0,0 +1,71 @@
+package io.ebeaninternal.server.deploy;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+
+import io.ebean.Platform;
+/**
+ * Class to hold the DDL-migration information that is needed to do correct alters.
+ * 
+ * @author Roland Praml, FOCONIS AG
+ */
+public class DbMigrationInfo {
+
+  private final List<String> preAdd;
+  private final List<String> postAdd;
+  private final List<String> preAlter;
+  private final List<String> postAlter;
+  private final List<Platform> platforms;  
+  
+  public DbMigrationInfo(String[] preAdd, String[] postAdd, String[] preAlter, String[] postAlter, Platform[] platforms) {
+    this.preAdd = toList(preAdd);
+    this.postAdd = toList(postAdd);
+    this.preAlter = toList(preAlter);
+    this.postAlter = toList(postAlter);
+    this.platforms = toList(platforms);
+  }
+
+  private <T> List<T> toList(T[] scripts) {
+    if (scripts.length == 0) {
+      return Collections.emptyList();
+    } else {
+      return Collections.unmodifiableList(Arrays.asList(scripts));
+    }
+  }
+  
+  public List<String> getPreAdd() {
+    return preAdd;
+  }
+  public List<String> getPostAdd() {
+    return postAdd;
+  }
+  public List<String> getPreAlter() {
+    return preAlter;
+  }
+  public List<String> getPostAlter() {
+    return postAlter;
+  }
+  public List<Platform> getPlatforms() {
+    return platforms;
+  }
+  
+  public String joinPlatforms() {
+    if (platforms.isEmpty()) {
+      return null;
+    } else {
+      StringBuilder sb = new StringBuilder();
+      for (Platform p : platforms) {
+        if (sb.length() > 0) {
+          sb.append(',');
+        }
+        sb.append(p.name().toLowerCase());
+      }
+      return sb.toString();
+    }
+  }
+
+
+}