Path Enumeration
Let's explore the first solution of the Naive Trees Antipattern.
We'll cover the following
One weakness of an Adjacency List is that it’s expensive to retrieve the ancestors of a given node in the tree. In Path Enumeration, this is solved by storing the string of ancestors as an attribute of each node.
Path Enumeration in directory hierarchies
We can see a form of Path Enumeration in directory hierarchies. A UNIX path like /usr/local/lib/
is a Path Enumeration of the filesystem, where usr
is the parent of local
, which in turn is the parent of lib
.
Creating Comments
table with a path
column
To employ the Path Enumeration solution, we can define a column called path
as a long VARCHAR
, instead of the parent_id
column, in the Comments
table. The string stored in this column is the sequence of ancestors of the current row, from the top of the tree down, just like a UNIX path. We can even choose / as a separator character.
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