DbMigration supports altering UniqueConstraints and foreign keys (#1279)

* NEW: Ebean reads version from pop.properties and prints it at start up

* DDL generation and migration can append a header and platformMigration is prepared to append epilog & prolog to scripts

* FIX: Set identity only, if it is not the platform default type

* Updated reference scripts

* ADD basic support for foreign key migration

* DbMigration detects alter foreign keys

* tests

src/main/java/io/ebeaninternal/dbmigration/model/MCompoundUniqueConstraint.java

@@ -1,5 +1,11 @@
 package io.ebeaninternal.dbmigration.model;
 
+import java.util.Arrays;
+import java.util.Objects;
+
+import io.ebeaninternal.dbmigration.ddlgeneration.platform.DdlHelp;
+import io.ebeaninternal.dbmigration.migration.AddUniqueConstraint;
+import io.ebeaninternal.dbmigration.migration.UniqueConstraint;
 /**
  * A unique constraint for multiple columns.
  * <p>
@@ -20,6 +26,8 @@ public class MCompoundUniqueConstraint {
    * The columns combined to be unique.
    */
   private final String[] columns;
+  
+  private String[] nullableColumns;
 
   public MCompoundUniqueConstraint(String[] columns, boolean oneToOne, String name) {
     this.name = name;
@@ -47,4 +55,78 @@ public class MCompoundUniqueConstraint {
   public String getName() {
     return name;
   }
+  public UniqueConstraint getUniqueConstraint() {
+    UniqueConstraint uq = new UniqueConstraint();
+    uq.setName(getName());
+    uq.setColumnNames(join(columns));
+    uq.setNullableColumns(join(nullableColumns));
+    uq.setOneToOne(isOneToOne());
+    return uq;
+  }
+  /**
+   * Return a AddUniqueConstraint migration for this constraint.
+   */
+  public AddUniqueConstraint addUniqueConstraint(String tableName) {
+    AddUniqueConstraint create = new AddUniqueConstraint();
+    create.setConstraintName(getName());
+    create.setTableName(tableName);
+    create.setColumnNames(join(columns));
+    create.setNullableColumns(join(nullableColumns));
+    create.setOneToOne(isOneToOne());
+    return create;
+  }
+
+  /**
+   * Create a AddUniqueConstraint migration with 'DROP CONSTRAINT' set for this index.
+   */
+  public AddUniqueConstraint dropUniqueConstraint(String tableName) {
+    AddUniqueConstraint dropUniqueConstraint = new AddUniqueConstraint();
+    dropUniqueConstraint.setConstraintName(name);
+    dropUniqueConstraint.setTableName(tableName);
+    dropUniqueConstraint.setColumnNames(DdlHelp.DROP_CONSTRAINT);
+    dropUniqueConstraint.setNullableColumns(join(nullableColumns));
+    return dropUniqueConstraint;
+  }
+  
+  public void setNullableColumns(String[] nullableColumns) {
+    if (nullableColumns != null && nullableColumns.length == 0) {
+      this.nullableColumns = null;
+    } else {
+      this.nullableColumns = nullableColumns;
+    }
+  }
+
+  private String join(String[] arr) {
+    if (arr == null) {
+      return "";
+    }
+    StringBuilder sb = new StringBuilder(50);
+    for (int i = 0; i < arr.length; i++) {
+      if (i > 0) {
+        sb.append(",");
+      }
+      sb.append(arr[i]);
+    }
+    return sb.toString();
+  }
+  
+  @Override
+  public int hashCode() {
+    return Arrays.hashCode(columns) + 31 * Objects.hash(name, oneToOne);
+  }
+  
+  @Override
+  public boolean equals(Object obj) {
+    if (obj == this) {
+      return true;
+    }
+    if (!(obj instanceof MCompoundUniqueConstraint)) {
+      return false;
+    }
+    MCompoundUniqueConstraint other = (MCompoundUniqueConstraint) obj;
+    return Arrays.equals(columns, other.columns)
+        && Arrays.equals(nullableColumns, other.nullableColumns)
+        && Objects.equals(name, other.name)
+        && oneToOne == other.oneToOne;
+  }
 }