#554 - DDL - DB Migration with @History and Postgres - views need to be dropped early to support migration changes

src/main/java/com/avaje/ebean/dbmigration/ddlgeneration/DdlWrite.java

@@ -12,12 +12,16 @@ public class DdlWrite {
 
   private final ModelContainer currentModel;
 
+  private final DdlBuffer applyDropDependencies;
+
   private final DdlBuffer apply;
 
   private final DdlBuffer applyForeignKeys;
 
   private final DdlBuffer applyHistory;
 
+  private final DdlBuffer rollbackDropDependencies;
+
   private final DdlBuffer rollbackForeignKeys;
 
   private final DdlBuffer rollback;
@@ -51,9 +55,11 @@ public class DdlWrite {
    */
   public DdlWrite(MConfiguration configuration, ModelContainer currentModel) {
     this.currentModel = currentModel;
+    this.applyDropDependencies = new BaseDdlBuffer(configuration);
     this.apply = new BaseDdlBuffer(configuration);
     this.applyForeignKeys = new BaseDdlBuffer(configuration);
     this.applyHistory = new BaseDdlBuffer(configuration);
+    this.rollbackDropDependencies = new BaseDdlBuffer(configuration);
     this.rollbackForeignKeys = new BaseDdlBuffer(configuration);
     this.rollback = new BaseDdlBuffer(configuration);
     this.drop = new BaseDdlBuffer(configuration);
@@ -77,7 +83,8 @@ public class DdlWrite {
   public boolean isApplyEmpty() {
     return apply.getBuffer().isEmpty()
         && applyForeignKeys.getBuffer().isEmpty()
-        && applyHistory.getBuffer().isEmpty();
+        && applyHistory.getBuffer().isEmpty()
+        && applyDropDependencies.getBuffer().isEmpty();
   }
 
   /**
@@ -85,9 +92,25 @@ public class DdlWrite {
    */
   public boolean isApplyRollbackEmpty() {
     return rollback.getBuffer().isEmpty()
-        && rollbackForeignKeys.getBuffer().isEmpty();
+        && rollbackForeignKeys.getBuffer().isEmpty()
+        && rollbackDropDependencies.getBuffer().isEmpty();
   }
 
+  /**
+   * Return the apply or rollback buffer.
+   */
+  public DdlBuffer buffer(boolean apply) {
+    return (apply) ? apply() : rollback();
+  }
+
+  /**
+   * Return the apply or rollback drop dependencies buffer.
+   */
+  public DdlBuffer dropDependencies(boolean apply) {
+    return (apply) ? applyDropDependencies() : rollbackDropDependencies();
+  }
+
+
   /**
    * Return true the drop buffers are empty.
    */
@@ -102,6 +125,13 @@ public class DdlWrite {
     return apply;
   }
 
+  /**
+   * Return the buffer that executes early to drop dependencies like views etc.
+   */
+  public DdlBuffer applyDropDependencies() {
+    return applyDropDependencies;
+  }
+
   /**
    * Return the buffer that APPLY DDL is written to for foreign keys and their associated indexes.
    * <p>
@@ -119,6 +149,13 @@ public class DdlWrite {
     return applyHistory;
   }
 
+  /**
+   * Return the buffer that rollback executes early to drop dependencies like views.
+   */
+  public DdlBuffer rollbackDropDependencies() {
+    return rollbackDropDependencies;
+  }
+
   /**
    * Return the buffer that ROLLBACK DDL is written to for foreign keys and associated indexes.
    */

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

@@ -121,7 +121,7 @@ public class PostgresHistoryDdl extends DbTriggerBasedHistoryDdl {
       apply.append("-- Regenerated ").append(procedureName).newLine();
       apply.append("-- changes: ").append(update.description()).newLine();
 
-      recreateHistoryView(apply, table.getName(), includedColumns);
+      recreateHistoryView(writer, true, table.getName(), includedColumns);
     }
 
     addFunction(apply, procedureName, historyTable, includedColumns);
@@ -134,7 +134,7 @@ 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);
+      recreateHistoryView(writer, false, table.getName(), includedColumns);
       addFunction(rollback, procedureName, historyTable, includedColumns);
     }
   }
@@ -143,11 +143,13 @@ public class PostgresHistoryDdl extends DbTriggerBasedHistoryDdl {
    * 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 {
+  private void recreateHistoryView(DdlWrite writer, boolean apply, String baseTableName, List<String> includedColumns) throws IOException {
 
-    buffer.append("drop view if exists ").append(baseTableName).append(viewSuffix).endOfStatement();
+    // we need to drop the view early/first before any changes to the tables etc
+    writer.dropDependencies(apply).append("drop view if exists ").append(baseTableName).append(viewSuffix).endOfStatement();
 
-    createWithHistoryView(buffer, baseTableName, includedColumns);
+    // recreate the view with specific columns specified (the columns generally are not dropped until later)
+    createWithHistoryView(writer.buffer(apply), baseTableName, includedColumns);
   }
 
   @Override

src/main/java/com/avaje/ebean/dbmigration/model/PlatformDdlWriter.java

@@ -116,6 +116,12 @@ public class PlatformDdlWriter {
   protected void writeApplyDdl(Writer writer, DdlWrite write) throws IOException {
 
     // merge the apply buffers in the appropriate order
+    if (!write.applyDropDependencies().isEmpty()) {
+      writer.append("-- drop dependencies\n");
+      writer.append(write.applyDropDependencies().getBuffer());
+      writer.append("\n");
+    }
+    writer.append("-- apply changes\n");
     writer.append(write.apply().getBuffer());
     writer.append(write.applyForeignKeys().getBuffer());
     writer.append(write.applyHistory().getBuffer());
@@ -127,6 +133,12 @@ public class PlatformDdlWriter {
   protected void writeApplyRollbackDdl(Writer writer, DdlWrite write) throws IOException {
 
     // merge the rollback buffers in the appropriate order
+    if (!write.rollbackDropDependencies().isEmpty()) {
+      writer.append("-- drop dependencies\n");
+      writer.append(write.rollbackDropDependencies().getBuffer());
+      writer.append("\n");
+    }
+    writer.append("-- reverse changes\n");
     writer.append(write.rollbackForeignKeys().getBuffer());
     writer.append(write.rollback().getBuffer());
   }