mono/mcs/class/referencesource/System.Data/System/Data/ProviderBase/DataReaderContainer.cs

//------------------------------------------------------------------------------
// <copyright file="DataReaderContainer.cs" company="Microsoft">
//      Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
// <owner current="true" primary="true">[....]</owner>
//------------------------------------------------------------------------------

namespace System.Data.ProviderBase {

    using System;
    using System.Data;
    using System.Data.Common;
    using System.Diagnostics;

    internal abstract class DataReaderContainer {

        protected readonly IDataReader _dataReader;
        protected int _fieldCount;

        static internal DataReaderContainer Create(IDataReader dataReader, bool returnProviderSpecificTypes) {
            if (returnProviderSpecificTypes) {
                DbDataReader providerSpecificDataReader = (dataReader as DbDataReader);
                if (null != providerSpecificDataReader) {
                    return new ProviderSpecificDataReader(dataReader, providerSpecificDataReader);
                }
            }
            return new CommonLanguageSubsetDataReader(dataReader);
        }

        protected DataReaderContainer(IDataReader dataReader) {
            Debug.Assert(null != dataReader, "null dataReader");
            _dataReader = dataReader;
        }

        internal int FieldCount {
            get {
                return _fieldCount;
            }
        }

        internal abstract bool ReturnProviderSpecificTypes { get; }
        protected abstract int VisibleFieldCount { get; }

        internal abstract Type GetFieldType(int ordinal);
        internal abstract object GetValue(int ordinal);
        internal abstract int GetValues(object[] values);

        internal string GetName(int ordinal) {
            string fieldName = _dataReader.GetName(ordinal);
            Debug.Assert(null != fieldName, "null GetName");
            return ((null != fieldName) ? fieldName : "");
        }
        internal DataTable GetSchemaTable() {
            return _dataReader.GetSchemaTable();
        }
        internal bool NextResult() {
            _fieldCount = 0;
            if (_dataReader.NextResult()) {
                _fieldCount = VisibleFieldCount;
                return true;
            }
            return false;
        }
        internal bool Read() {
            return _dataReader.Read();
        }

        private sealed class ProviderSpecificDataReader : DataReaderContainer {
            private DbDataReader _providerSpecificDataReader;

            internal ProviderSpecificDataReader(IDataReader dataReader, DbDataReader dbDataReader) : base(dataReader) {
                Debug.Assert(null != dataReader, "null dbDataReader");
                _providerSpecificDataReader = dbDataReader;
                _fieldCount = VisibleFieldCount;
            }

            internal override bool ReturnProviderSpecificTypes {
                get {
                    return true;
                }
            }
            protected override int VisibleFieldCount {
                get {
                    int fieldCount = _providerSpecificDataReader.VisibleFieldCount;
                    Debug.Assert(0 <= fieldCount, "negative FieldCount");
                    return ((0 <= fieldCount) ? fieldCount : 0);
                }
            }

            internal override Type GetFieldType(int ordinal) {
                Type fieldType = _providerSpecificDataReader.GetProviderSpecificFieldType(ordinal);
                Debug.Assert(null != fieldType, "null FieldType");
                return fieldType;
            }
            internal override object GetValue(int ordinal) {
                return _providerSpecificDataReader.GetProviderSpecificValue(ordinal);
            }
            internal override int GetValues(object[] values) {
                return _providerSpecificDataReader.GetProviderSpecificValues(values);
            }
        }

        private sealed class CommonLanguageSubsetDataReader : DataReaderContainer {

            internal CommonLanguageSubsetDataReader(IDataReader dataReader ) : base(dataReader) {
                _fieldCount = VisibleFieldCount;
            }

            internal override bool ReturnProviderSpecificTypes {
                get {
                    return false;
                }
            }
            protected override int VisibleFieldCount {
                get {
                    int fieldCount = _dataReader.FieldCount;
                    Debug.Assert(0 <= fieldCount, "negative FieldCount");
                    return ((0 <= fieldCount) ? fieldCount : 0);
                }
            }

            internal override Type GetFieldType(int ordinal) {
                return _dataReader.GetFieldType(ordinal);
            }
            internal override object GetValue(int ordinal) {
                return _dataReader.GetValue(ordinal);
            }
            internal override int GetValues(object[] values) {
                return _dataReader.GetValues(values);
            }
        }
    }
}