JCR -ModeShape : Create unique node names

Question

I need to add some node[file] to a node [folder]. but maybe some of these have the same name. like this:

attach\fileName1
attach\fileName2
attach\fileName1

I want to have an unique ID (Primary key) instead of the file name because, I use this path in another node. Is there any way to create something like auto generated ID in JCR? Or I have to manage it pragmatical?

Thanks in advance

Answer 1

JCR's standard approach for child nodes having the same name is to use same-name-siblings, or SNS (see here and here). However, their use is generally discouraged, because as the children of a node are moved, renamed, inserted, and deleted, the same-name-sibling index (and thus the path) for a given child node may change.

The JCR 2.0 API also does not define a way to automatically generate unique child node names. (JSR-333, or "JCR 2.1", is nearing final adoption and will add a way to add child nodes with unique names in an automated way. ModeShape plans to support JSR-333 in 4.0; check our roadmap for a schedule.)

So, given this, there are two ways to accomplish what you are asking, and both techniques work well in a ModeShape cluster.

Generate your own unique names

The standard nt:folder node type does not allow child nodes with same-name-siblings. After all, the nt:folder and nt:file where designed to behave like most file systems, and most of those do not allow files/folders with the same name. Therefore, when you create a node with a primary type of nt:folder, then every child must have a unique name.

One very simple way to create a unique name for a child is to use the standard java.util.UUID class. Simply generate a unique ID, and use the string form within the new child's name.

Use Same Name Siblings (SNS)

Alternatively, if you'd rather have the repository manage the uniqueness of the child node names via SNS indexes and can live with the disadvantages of SNS nodes, then simply define a custom node type that makes this possible. For example, here is a node type definition that subtypes nt:hierarchyNode (which is the supertype of both nt:folder and nt:file), and is thus similar but unrelated to nt:folder:

[acme:folder] > nt:hierarchyNode 
+ * (nt:hierarchyNode) version sns

(Your custom node type is not required to extend nt:hierarchyNode, but doing so makes it possible for nt:folder to contain nodes of type nt:file, nt:folder, and acme:folder.)

Once this node type definition is registered, simply create your folder nodes with that custom type as their primary type (or change the primary type later, which ModeShape does support).

Answer 2

You can do this by using JcrUtils you would be able to specify your name hint for the node, i.e your "fileName" and JcrUtil will preappend a number to it resulting in something like "fileName0", bellow will do exactly what you are asking for:

JcrUtils.getOrCreateUniqueByPath(attach, "fileName", "type goes here");