internal async Task <ReadOnlyCollection <NpgsqlDbColumn> > GetColumnSchema(bool async, CancellationToken cancellationToken = default)
{
// This is mainly for Amazon Redshift
var oldQueryMode = _connection.PostgreSqlVersion < new Version(8, 2);
var numFields = _rowDescription.Count;
var result = new List <NpgsqlDbColumn?>(numFields);
for (var i = 0; i < numFields; i++)
{
result.Add(null);
}
var populatedColumns = 0;
if (_fetchAdditionalInfo)
{
// We have two types of fields - those which correspond to actual database columns
// and those that don't (e.g. SELECT 8). For the former we load lots of info from
// the backend (if fetchAdditionalInfo is true), for the latter we only have the RowDescription
var columnFieldFilter = _rowDescription
.Where(f => f.TableOID != 0) // Only column fields
.Select(c => $"(attr.attrelid={c.TableOID} AND attr.attnum={c.ColumnAttributeNumber})")
.Join(" OR ");
if (columnFieldFilter != string.Empty)
{
var query = oldQueryMode
? GenerateOldColumnsQuery(columnFieldFilter)
: GenerateColumnsQuery(_connection.PostgreSqlVersion, columnFieldFilter);
using var scope = new TransactionScope(
TransactionScopeOption.Suppress,
async ? TransactionScopeAsyncFlowOption.Enabled : TransactionScopeAsyncFlowOption.Suppress);
using var connection = (NpgsqlConnection)((ICloneable)_connection).Clone();
await connection.Open(async, cancellationToken);
using var cmd = new NpgsqlCommand(query, connection);
using var reader = await cmd.ExecuteReader(CommandBehavior.Default, async, cancellationToken);
while (async ? await reader.ReadAsync(cancellationToken): reader.Read())
{
var column = LoadColumnDefinition(reader, _connection.Connector !.TypeMapper.DatabaseInfo, oldQueryMode);
for (var ordinal = 0; ordinal < numFields; ordinal++)
{
var field = _rowDescription[ordinal];
if (field.TableOID == column.TableOID &&
field.ColumnAttributeNumber == column.ColumnAttributeNumber)
{
populatedColumns++;
if (column.ColumnOrdinal.HasValue)
{
column = column.Clone();
}
// The column's ordinal is with respect to the resultset, not its table
column.ColumnOrdinal = ordinal;
result[ordinal] = column;
}
}
}
}
}
// We had some fields which don't correspond to regular table columns (or fetchAdditionalInfo is false).
// Fill in whatever info we have from the RowDescription itself
for (var i = 0; i < numFields; i++)
{
var column = result[i];
var field = _rowDescription[i];
if (column is null)
{
column = SetUpNonColumnField(field);
column.ColumnOrdinal = i;
result[i] = column;
populatedColumns++;
}
column.ColumnName = field.Name;
column.IsAliased = column.BaseColumnName is null ? default(bool?) : (column.BaseColumnName != column.ColumnName);
}
if (populatedColumns != numFields)
{
throw new NpgsqlException("Could not load all columns for the resultset");
}
return(result.AsReadOnly() !);
}
