Testcase for ebean with circular dependences

[tobias-]

Two failing test cases.

1. While the javax.persistance api discourages the use of bidirectional
   cascades, it does not prohibit them. They're very useful and natural
   if you think of the database as a graph instead of a tree.
   test case 1 (testCircularCascade) tests this.
2. Second test case fetches the child, but saves the parent. If used like
   that, the child will not have it's changes saved, even with cascade = ALL.

[rPraml]

I'm not happy with this change

1. why do you need to replace with T? (btw when replacing single characters it is better to use replace(' ', 'T'))
2. the change makes the dateTimeParser.parse method obsolete. So it would be better to change the 'parse' implementation.

What was the problem here? I assume, the precision of fractions of the DateTimeParser. Newer java versions (11+) probable needs up to 9 digits: `yyyy-MM-dd'T'HH:mm:ss.SSSSSSSSS'Z'
@rbygrave I think it would be a good idea to refactor the DateTimeParser, so that it uses Instant.parse instead of SimpleDateFormat

[rbygrave]

good idea to refactor the DateTimeParser, so that it uses Instant.parse instead of SimpleDateFormat

Yes, I agree @rPraml @tobias- ... Refactoring UtilDateTimeParser to use Instant.parse() looks like the good option.

[tobias-]

@rPraml @rbygrave Sorry, I managed to put extra stuff on this branch (it's been force pushed away not long after @rPraml commented on this PR). The java.time issue (#1725) is PR #1724 and nothing else. This PR is about test cases for circular dependencies.

[rbygrave]

Nice tests. I should get to them shortly (tomorrow night).

[tobias-]

@rbygrave I can make these test cases work by moving the request.executeOrQueue() to before saveAssocOne(). That makes a lot of other test cases fail though. Below is what I mean.

diff --git a/src/main/java/io/ebeaninternal/server/persist/DefaultPersister.java b/src/main/java/io/ebeaninternal/server/persist/DefaultPersister.java
index 0d02a49ef..3d8134b7b 100644
--- a/src/main/java/io/ebeaninternal/server/persist/DefaultPersister.java
+++ b/src/main/java/io/ebeaninternal/server/persist/DefaultPersister.java
@@ -546,10 +546,6 @@ public final class DefaultPersister implements Persister {
     }
     request.flagUpdate();
     try {
-      if (request.isPersistCascade()) {
-        // save associated One beans recursively first
-        saveAssocOne(request);
-      }
 
       if (request.isDirty()) {
         request.executeOrQueue();
@@ -558,6 +554,11 @@ public final class DefaultPersister implements Persister {
         logger.debug(Message.msg("persist.update.skipped", request.getBean()));
       }
 
+      if (request.isPersistCascade()) {
+        // save associated One beans recursively first
+        saveAssocOne(request);
+      }
+
       if (request.isPersistCascade()) {
         // save all the beans in assocMany's after
         saveAssocMany(request);

[rbygrave]

Note that there is not a fix for testFetchChildModifyChildSaveParent() yet. This test just marked with @Ignore until I can look at it more.