Class ResultReader

Namespace

YndigoBlue.Velocity.Engine

Assembly

YndigoBlue.Velocity.dll

Provides forward-only, read-once iteration over query results with minimal memory overhead.

public class ResultReader : IEnumerable<Result>, IEnumerable, IDisposable

Inheritance

object

ResultReader

Implements

IEnumerable<Result>

IEnumerable

IDisposable

Examples

var conn = new PostgreSqlDatasourceConnection
{
    Hostname = "localhost",
    Database = "mydatabase",
    Username = "user",
    Password = "password"
};

using (var manager = new Manager(conn))
{
    var schema = manager.LoadSchema("public");
    var usersTable = schema["users"];

    var query = new Query()
        .Select([usersTable["id"], usersTable["name"], usersTable["email"]])
        .From(usersTable)
        .Where(new Criterion<bool>(usersTable["active"], ConditionalType.Equals, true));

    // Use ResultReader for large datasets
    using (ResultReader reader = manager.ExecuteReader(query))
    {
        foreach (Result row in reader)
        {
            int id = row.GetFieldInteger("id");
            string name = row.GetFieldVarChar("name");
            string email = row.GetFieldVarChar("email");

            Console.WriteLine($"{id}: {name} ({email})");
        }
    } // Reader and connection are disposed here
}

Remarks

ResultReader is a connected, streaming result processor that wraps a database reader for efficient memory usage when processing large result sets. Unlike ResultSet which loads all results into memory, ResultReader processes rows one at a time as they're retrieved from the database.

Key Characteristics:

• Forward-only iteration - cannot go backwards or re-read results
• Minimal memory footprint - only one row in memory at a time
• Requires active database connection during iteration
• Must be disposed to release database resources
• Ideal for processing large datasets or streaming operations

When to Use:

• Processing large result sets where memory is a concern
• Streaming data transformations or exports
• Sequential processing where random access isn't needed
• Real-time data processing or ETL operations

Use ResultSet instead when:

• Need random access to results (indexing)
• Need to iterate multiple times
• Need to filter or sort results in memory
• Result set is small enough to fit in memory

Methods

BindColumn<T>()

Binds the first column from query results to a typed enumerable collection.

BindColumn<T>(int)

Binds a single column from query results to a typed enumerable collection by column index.

BindColumn<T>(string)

Binds a single column from query results to a typed enumerable collection by column name.

BindResults<T>(BindingType)

Binds query results to a typed enumerable collection using the specified binding strategy.

Dispose()

Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.

GetEnumerator()

Returns an enumerator that iterates through the collection.

GetGeoJSON(string, bool)

Converts query results containing geospatial data to GeoJSON format.