How to read array field from database using c#?

Question

I am using C# with postgresql. In the database I have a table named test and in this table I have a column named arr that it's datatype is double[] and I stored multiple record like this {1, 1, 2, 3, 0, 5, 1, 4}. Now, how to return those records into C# program and stored in a list for example List<double[]> arr1 = new List<double[]>();

Who can help me?

You should add your code then we can help you, because there are a dozen of ways to do this, e.g. using Linq, running query statements directly, getting data from a service provider, etc. — Mohsen Kamrani
– Mohsen Kamrani, Commented Sep 5, 2016 at 23:07

Hambone · Accepted Answer · 2021-02-18 13:16:19Z

7

For array datatypes, all you have to do is cast the result as an array of double:

NpgsqlConnection conn = new NpgsqlConnection(connectionString);
conn.Open();

NpgsqlCommand cmd = new NpgsqlCommand("select arr from test", conn);
NpgsqlDataReader reader = cmd.ExecuteReader();

while (reader.Read())
{
    double[] myArray = (double[])reader.GetValue(0);
    // do your bidding
}

reader.Close();

-- EDIT 2/18/2021 --

As of Npgsql 5.0, the above method seems to work most of the time, but the documents specify a different way to extract array datatypes:

double[] myArray = reader.GetFieldValue<double[]>(0)

edited Feb 18, 2021 at 13:16

answered Sep 16, 2016 at 9:57

Hambone

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Vural · Accepted Answer · 2016-09-05 11:35:23Z

0

Here is a walkthrough, Using PostgreSQL in your C# (.NET): Using PostgreSQL in your C# (.NET)

You will need to give us some specific problems that you are having so we can help solve the problem.

answered Sep 5, 2016 at 11:35

Vural

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2 Comments

zana Over a year ago

I am using this idea

List<double[]> arr1 = new List<double[]>();              foreach (DataRow row in ds.Tables["test"].Rows)             {                    arr1.Add(row["arr"].Select(s => Double.Parse(s)).ToList());             }

but, I got error!!

zana Over a year ago

Error 2 'System.Linq.Queryable.Select<TSource,TResult>(System.Linq.IQueryable<TSource>, System.Linq.Expressions.Expression<System.Func<TSource,TResult>>)' is a 'method', which is not valid in the given context C:\Users\PCLORD\Desktop\ShowImg\ShowImg\Default.aspx.cs 103 39 ShowImg

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