Postgres integer arrays as parameters?

Question

I understand that in Postgres pure, you can pass an integer array into a function but that this isn't supported in the .NET data provider Npgsql.

I currently have a DbCommand into which I load a call to a stored proc, add in a parameter and execute scalar to get back an Id to populate an object with.

This now needs to take n integers as arguments. These are used to create child records linking the newly created record by it's id to the integer arguments.

Ideally I'd rather not have to make multiple ExecuteNonQuery calls on my DbCommand for each of the integers, so I'm about to build a csv string as a parameter that will be split on the database side.

I normally live in LINQ 2 SQL savouring the Db abstraction, working on this project with manual data access it's all just getting a bit dirty, how do people usually go about passing these kinds of parameters into postgres?

Answer 1

See: http://www.postgresql.org/docs/9.1/static/arrays.html

If your non-native driver still does not allow you to pass arrays, then you can:

• pass a string representation of an array (which your stored procedure can then parse into an array -- see string_to_array)

  CREATE FUNCTION my_method(TEXT) RETURNS VOID AS $$ 
  DECLARE
         ids INT[];
  BEGIN
         ids = string_to_array($1,',');
         ...
  END $$ LANGUAGE plpgsql;
  

  then

  SELECT my_method(:1)
  

  with :1 = '1,2,3,4'

• rely on Postgres itself to cast from a string to an array

  CREATE FUNCTION my_method(INT[]) RETURNS VOID AS $$ 
         ...
  END $$ LANGUAGE plpgsql;
  

  then

  SELECT my_method('{1,2,3,4}')
  

• choose not to use bind variables and issue an explicit command string with all parameters spelled out instead (make sure to validate or escape all parameters coming from outside to avoid SQL injection attacks.)

  CREATE FUNCTION my_method(INT[]) RETURNS VOID AS $$ 
         ...
  END $$ LANGUAGE plpgsql;
  

  then

  SELECT my_method(ARRAY [1,2,3,4])
  

Answer 2

I realize this is an old question, but it took me several hours to find a good solution and thought I'd pass on what I learned here and save someone else the trouble. Try, for example,

SELECT * FROM some_table WHERE id_column = ANY(@id_list)

where @id_list is bound to an int[] parameter by way of

command.Parameters.Add("@id_list", NpgsqlDbType.Array | NpgsqlDbType.Integer).Value = my_id_list;

where command is a NpgsqlCommand (using C# and Npgsql in Visual Studio).

Answer 3

You can always use a properly formatted string. The trick is the formatting.

command.Parameters.Add("@array_parameter", string.Format("{{{0}}}", string.Join(",", array));

Note that if your array is an array of strings, then you'll need to use array.Select(value => string.Format("\"{0}\", value)) or the equivalent. I use this style for an array of an enumerated type in PostgreSQL, because there's no automatic conversion from the array.

In my case, my enumerated type has some values like 'value1', 'value2', 'value3', and my C# enumeration has matching values. In my case, the final SQL query ends up looking something like (E'{"value1","value2"}'), and this works.