I can create a function that takes a two dimension int array:
CREATE FUNCTION twodims(int[][]) RETURNS void AS ...
but there's nothing stopping me from calling this function with an
arbitrary number of dimensions on the array.
I'd like to map a parameter like the one above to a corresponding
representation in Java (it would be int[][] there too). As it turns out,
I can't do that. PostgreSQL will not store any information that can tell
me how many dimensions that where used in the declaration, i.e. it's
impossible to write a language VALIDATOR that, based on the information
in pg_proc, builds a signature where the number of dimensions is reflected.
This leaves me with two choices:
Only allow arrays with one dimension unless the parameter is of a domain
type (domains are apparently stored with the actual number of
dimensions). Any call that uses an array parameter with more then one
dimension will yield an exception.
--OR--
Always map to Object[] instead of mapping to the correct type, . This
will work since an array in Java is also an Object and all primitive
types can be represented as objects (i.e. int can be a
java.lang.Integer). The strong typing and the ability to use primitives
are lost however.
I'm leaning towards #1 and hoping that PostgreSQL will enhance the
parameter type declarations to include the dimensions in future releases.
... After some more testing ...
Unfortunately, I run into problems even when I use domains. Consider the
following:
thhal=# CREATE DOMAIN twodims as int[][];
CREATE DOMAIN
thhal=# SELECT typndims FROM pg_type WHERE typname = 'twodims';
typndims
----------
2
(1 row)
thhal=# SELECT array_dims('{{{1,2,3},{3,4,3}},{{5,3,2},{9,9,9}}}'::twodims);
array_dims
-----------------
[1:2][1:2][1:3]
(1 row)
IMO, there is something seriously wrong here. Clearly the number of
dimensions is a property of the type. Any array with a different number
of dimensions should yield an error or at least be coerced into the
right number of dimensions.
Kind Regards,
Thomas Hallgren
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TIP 6: explain analyze is your friend
