#553 - DDL - DB Migration with @History and Postgres needs to re-create the "with_history" view when columns dropped

src/main/java/com/avaje/ebean/dbmigration/ddlgeneration/platform/DbTriggerBasedHistoryDdl.java

@@ -191,6 +191,25 @@ public abstract class DbTriggerBasedHistoryDdl implements PlatformHistoryDdl {
         .endOfStatement().end();
   }
 
+  /**
+   * Create or replace the with_history view with explicit columns.
+   */
+  protected void createWithHistoryView(DdlBuffer apply, String baseTableName, List<String> columns) throws IOException {
+
+    apply.append("create or replace view ").append(baseTableName).append(viewSuffix).append(" as select ");
+    appendColumnNames(apply, columns, "");
+    appendSysPeriodColumns(apply, ", ");
+    apply.append(" from ").append(baseTableName).append(" union all select ");
+    appendColumnNames(apply, columns, "");
+    appendSysPeriodColumns(apply, ", ");
+    apply.append(" from ").append(baseTableName).append(historySuffix).endOfStatement().end();
+  }
+
+  protected void appendSysPeriodColumns(DdlBuffer apply, String prefix) throws IOException {
+    appendColumnName(apply, prefix, sysPeriodStart);
+    appendColumnName(apply, prefix, sysPeriodEnd);
+  }
+
   protected void dropHistoryTableEtc(DdlBuffer buffer, String baseTableName) throws IOException {
 
     buffer.append("drop view ").append(baseTableName).append(viewSuffix).endOfStatement();
@@ -203,8 +222,6 @@ public abstract class DbTriggerBasedHistoryDdl implements PlatformHistoryDdl {
     buffer.append("alter table ").append(baseTableName).append(" drop column ").append(sysPeriodEnd).endOfStatement();
   }
 
-  //protected abstract void addFunction(DdlBuffer apply, String procedureName, String historyTable, List<String> includedColumns) throws IOException;
-
   protected void appendInsertIntoHistory(DdlBuffer buffer, String historyTable, List<String> columns) throws IOException {
 
     buffer.append("    insert into ").append(historyTable).append(" (").append(sysPeriodStart).append(",").append(sysPeriodEnd).append(",");
@@ -225,6 +242,16 @@ public abstract class DbTriggerBasedHistoryDdl implements PlatformHistoryDdl {
     }
   }
 
+  /**
+   * Append a single column to the buffer if it is not null.
+   */
+  protected void appendColumnName(DdlBuffer buffer, String prefix, String columnName) throws IOException {
+
+    if (columnName != null) {
+      buffer.append(prefix).append(columnName);
+    }
+  }
+
   /**
    * Return the list of included columns in order.
    */

src/main/java/com/avaje/ebean/dbmigration/ddlgeneration/platform/PostgresHistoryDdl.java

@@ -45,6 +45,11 @@ public class PostgresHistoryDdl extends DbTriggerBasedHistoryDdl {
     }
   }
 
+  @Override
+  protected void appendSysPeriodColumns(DdlBuffer apply, String prefix) throws IOException {
+    appendColumnName(apply, prefix, sysPeriod);
+  }
+
   @Override
   protected void dropSysPeriodColumns(DdlBuffer buffer, String baseTableName) throws IOException {
     buffer.append("alter table ").append(baseTableName).append(" drop column ").append(sysPeriod).endOfStatement();
@@ -115,11 +120,12 @@ public class PostgresHistoryDdl extends DbTriggerBasedHistoryDdl {
     if (update != null) {
       apply.append("-- Regenerated ").append(procedureName).newLine();
       apply.append("-- changes: ").append(update.description()).newLine();
+
+      recreateHistoryView(apply, table.getName(), includedColumns);
     }
 
     addFunction(apply, procedureName, historyTable, includedColumns);
 
-
     if (update != null) {
       // put a reverted version into the rollback buffer
       update.toRevertedColumns(includedColumns);
@@ -128,10 +134,22 @@ public class PostgresHistoryDdl extends DbTriggerBasedHistoryDdl {
       rollback.append("-- Revert regenerated ").append(procedureName).newLine();
       rollback.append("-- revert changes: ").append(update.description()).newLine();
 
+      recreateHistoryView(rollback, table.getName(), includedColumns);
       addFunction(rollback, procedureName, historyTable, includedColumns);
     }
   }
 
+  /**
+   * For postgres we need to drop and recreate the view. Well, we could add columns to the end of the view
+   * but otherwise we need to drop and create it.
+   */
+  private void recreateHistoryView(DdlBuffer buffer, String baseTableName, List<String> includedColumns) throws IOException {
+
+    buffer.append("drop view if exists ").append(baseTableName).append(viewSuffix).endOfStatement();
+
+    createWithHistoryView(buffer, baseTableName, includedColumns);
+  }
+
   @Override
   protected void appendInsertIntoHistory(DdlBuffer buffer, String historyTable, List<String> columns) throws IOException {