Java – JCR 170 Data modeling: Node names

data-modelingjackrabbitjavajcr

The situation:
Lets say we are implementing a blog engine based on JCR with support for localization.
The content structure looks something like this /blogname/content/[node name]

The problem:
What is the best way to name the content nodes (/blogname/content/[nodename]) to satisfy the following requirements:

The node name must be usable in HTML to support REST like URLs i.e.: blogname.com/content/nodename should point to a single content item.
The above requirement must not produce ugly URLs i.e.: /content/node_name is good, /content/node%20name is bad.
Programmatic retrieval should be easy given the node name i.e.: //content[@node_name=some-name]
The naming scheme must guarantee node name uniqueness.

PS: The JCR implementation used is JackRabbit

Best Solution

For 1. to 3. the answer is simple: just use characters you want to see in the node name, ie. escape whatever input string you have (eg. the blog post title) against a restricted character set such as the one for URIs.

For example, do not allow spaces (which are allowed for JCR node names, but would produce the ugly %20 in URLs) and other chars that must be encoded in URLs. You can remove those chars or simply replace them with a underscore, because that looks good in most cases.

Regarding unique names (4.), you can either include the current time incl. milliseconds into it or you explicitly check for collisions. The first might look a bit ugly, but should probably never fail for a blog scenario. The latter can be done by reacting upon the exception thrown if a node with such a name already exists and adding eg. an incrementing counter and try again (eg. my_great_post1, my_great_post2, etc.). You can also lock the parent node so that only one session can actually add a node at the same time, which avoids a trial loop, but comes at the cost of blocking.

Note: //content[@node_name=some-name] is not a valid JCR Xpath query. You probably want to use /jcr:root/content//some-name for that.

Related Solutions

Java – How to you change the name of a JCR node

The Jackrabbit Wiki provides an example:

void rename(Node node, String newName) throws RepositoryException 
    {
        node.getSession().move(node.getPath(), node.getParent().getPath() + "/" + newName);
        // Don't forget - not necessarily here at this place:
        // node.getSession().save();
    }

Data Modeling with Kafka? Topics and Partitions

When structuring your data for Kafka it really depends on how it´s meant to be consumed.

In my mind, a topic is a grouping of messages of a similar type that will be consumed by the same type of consumer so in the example above, I would just have a single topic and if you´ll decide to push some other kind of data through Kafka, you can add a new topic for that later.

Topics are registered in ZooKeeper which means that you might run into issues if trying to add too many of them, e.g. the case where you have a million users and have decided to create a topic per user.

Partitions on the other hand is a way to parallelize the consumption of the messages. The total number of partitions in a broker cluster need to be at least the same as the number of consumers in a consumer group to make sense of the partitioning feature. Consumers in a consumer group will split the burden of processing the topic between themselves according to the partitioning so that one consumer will only be concerned with messages in the partition itself is "assigned to".

Partitioning can either be explicitly set using a partition key on the producer side or if not provided, a random partition will be selected for every message.

Best Solution

Related Solutions

Java – How to you change the name of a JCR node

Data Modeling with Kafka? Topics and Partitions

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