PostgreSQL – How to Pass a Type as an Argument in Functions

Views are implemented as table plus rewrite rule in Postgres. Details in the manual, chapter Views and the Rule System.

The tricky part: not the view itself depends on involved functions, only the rewrite rule does. So this query should be your solution:

SELECT r.ev_class::regclass AS view, d.refobjid::regprocedure AS function
FROM   pg_rewrite r
JOIN   pg_depend  d ON d.objid = r.oid 
                   AND d.refclassid = 'pg_proc'::regclass  -- only functions
WHERE  r.ev_class = 'v123'::regclass;  -- name of view here (optionally schema-qualified)

Returns all user-defined functions (excluding built-in functions).

The query assumes you did not define any additional rules for the view. Else filter the one with rulename = '_RETURN', which is the default name for the rewrite rules of a view.

The cast to regprocedure (not just regproc) returns the function with argument types, uniquely identifying it. The name is schema-qualified automatically if the current search_path would not resolve differently otherwise.

I would never use these objects. They simply don't seem that useful. That said, PostgreSQL does have a method of passing a table to a function via jsonb. Likely that would be the ideal solution for you if you're looking to get the functionality described in Passing a Table-Valued Parameter to a Stored Procedure. All you'd have to do is map the DataTable to JSON, and then pass the JSON to the function.

To convert a Datatable to JSON you can use JSON.net. See also these Stack Overflow answers.

• How to convert datatable to json string using json.net?

• Convert datatable to JSON in C#

If the Datatable is too big to serialize to JSON, you may have to create a Foreign Data Wrapper around something that exports the DataRow objects, this would start you down the path mentioned in "Streaming Rows with a DataReader". Though if you don't need a server/client model, you can always dump the DataTable to CSV and read it with a Foreign Data Wrapper: to go down that route check out file-fdw.

I actually tried this. I ran into a ton of problems.

1. It wasn't even easy figuring out how to install a package with nuGet,
2. Having installed nuGet, despite being the #1 package on nuGet, it doesn't yet work with .NET Core 2.x
3. Installing the beta version of nuGet, I got it to work.

Converting a DataTable to JSON with .NET Core 2.x,

using System;
using System.Data;
using Newtonsoft.Json;

class Program
{
  static void Main()
  {
    // Get the DataTable.
    DataTable table = GetTable();
    // ... Use the DataTable here with SQL.
    string json = JsonConvert.SerializeObject(table, Formatting.Indented);
    Console.WriteLine(json);

  }

  static DataTable GetTable()
  {
    // Here we create a DataTable with four columns.
    DataTable table = new DataTable();
    table.Columns.Add("Dosage", typeof(int));
    table.Columns.Add("Drug", typeof(string));
    table.Columns.Add("Patient", typeof(string));
    table.Columns.Add("Date", typeof(DateTime));

    // Here we add five DataRows.
    table.Rows.Add(25, "Indocin", "David", DateTime.Now);
    table.Rows.Add(50, "Enebrel", "Sam", DateTime.Now);
    table.Rows.Add(10, "Hydralazine", "Christoff", DateTime.Now);
    table.Rows.Add(21, "Combivent", "Janet", DateTime.Now);
    table.Rows.Add(100, "Dilantin", "Melanie", DateTime.Now);

    return table;
  }
}

You'd still have to connect to the db and drop the json into an INSERT statement, but that should be easily done.

cmd.CommandText = "SELECT * FROM myfunc(@json)";
cmd.Parameters.AddWithValue("json", json);

Define myfunc(jsonb) on the server, and you should be good: you've passed a DataTable into PostgreSQL.