DbDataReaderExtensions.cs

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using System.Collections.Generic;
using System.Collections.ObjectModel;
 
namespace System.Data.Common;
 
public static class DbDataReaderExtensions
{
    private sealed class DataRowDbColumn : DbColumn
    {
        private readonly DataColumnCollection _schemaColumns;
 
        private readonly DataRow _schemaRow;
 
        public DataRowDbColumn(DataRow readerSchemaRow, DataColumnCollection readerSchemaColumns)
        {
            _schemaRow = readerSchemaRow;
            _schemaColumns = readerSchemaColumns;
            PopulateFields();
        }
 
        private void PopulateFields()
        {
            base.AllowDBNull = GetDbColumnValue<bool?>(SchemaTableColumn.AllowDBNull);
            base.BaseCatalogName = GetDbColumnValue<string>(SchemaTableOptionalColumn.BaseCatalogName);
            base.BaseColumnName = GetDbColumnValue<string>(SchemaTableColumn.BaseColumnName);
            base.BaseSchemaName = GetDbColumnValue<string>(SchemaTableColumn.BaseSchemaName);
            base.BaseServerName = GetDbColumnValue<string>(SchemaTableOptionalColumn.BaseServerName);
            base.BaseTableName = GetDbColumnValue<string>(SchemaTableColumn.BaseTableName);
            base.ColumnName = GetDbColumnValue<string>(SchemaTableColumn.ColumnName);
            base.ColumnOrdinal = GetDbColumnValue<int?>(SchemaTableColumn.ColumnOrdinal);
            base.ColumnSize = GetDbColumnValue<int?>(SchemaTableColumn.ColumnSize);
            base.IsAliased = GetDbColumnValue<bool?>(SchemaTableColumn.IsAliased);
            base.IsAutoIncrement = GetDbColumnValue<bool?>(SchemaTableOptionalColumn.IsAutoIncrement);
            base.IsExpression = GetDbColumnValue<bool>(SchemaTableColumn.IsExpression);
            base.IsHidden = GetDbColumnValue<bool?>(SchemaTableOptionalColumn.IsHidden);
            base.IsIdentity = GetDbColumnValue<bool?>("IsIdentity");
            base.IsKey = GetDbColumnValue<bool?>(SchemaTableColumn.IsKey);
            base.IsLong = GetDbColumnValue<bool?>(SchemaTableColumn.IsLong);
            base.IsReadOnly = GetDbColumnValue<bool?>(SchemaTableOptionalColumn.IsReadOnly);
            base.IsUnique = GetDbColumnValue<bool?>(SchemaTableColumn.IsUnique);
            base.NumericPrecision = GetDbColumnValue<int?>(SchemaTableColumn.NumericPrecision);
            base.NumericScale = GetDbColumnValue<int?>(SchemaTableColumn.NumericScale);
            base.UdtAssemblyQualifiedName = GetDbColumnValue<string>("UdtAssemblyQualifiedName");
            base.DataType = GetDbColumnValue<Type>(SchemaTableColumn.DataType);
            base.DataTypeName = GetDbColumnValue<string>("DataTypeName");
        }
 
        private T GetDbColumnValue<T>(string columnName)
        {
            if (_schemaColumns.Contains(columnName))
            {
                object obj = _schemaRow[columnName];
                if (obj is T)
                {
                    return (T)obj;
                }
            }
            return default(T);
        }
    }
 
    public static ReadOnlyCollection<DbColumn> GetColumnSchema(this DbDataReader reader)
    {
        if (reader == null)
        {
            throw new ArgumentNullException("reader");
        }
        if (reader is IDbColumnSchemaGenerator dbColumnSchemaGenerator)
        {
            return dbColumnSchemaGenerator.GetColumnSchema();
        }
        return GetColumnSchemaCompatibility(reader);
    }
 
    public static bool CanGetColumnSchema(this DbDataReader reader)
    {
        return true;
    }
 
    private static ReadOnlyCollection<DbColumn> GetColumnSchemaCompatibility(DbDataReader reader)
    {
        List<DbColumn> list = new List<DbColumn>();
        DataTable schemaTable = reader.GetSchemaTable();
        if (schemaTable != null)
        {
            DataColumnCollection columns = schemaTable.Columns;
            foreach (DataRow row in schemaTable.Rows)
            {
                list.Add(new DataRowDbColumn(row, columns));
            }
        }
        return new ReadOnlyCollection<DbColumn>(list);
    }
}