DataRowExtensions.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Diagnostics.CodeAnalysis;
using System.Runtime.CompilerServices;

namespace System.Data
{
    /// <summary>
    /// This static class defines the DataRow extension methods.
    /// </summary>
    public static class DataRowExtensions
    {
        /// <summary>
        /// This method provides access to the values in each of the columns in a given row.
        /// This method makes casts unnecessary when accessing columns.
        /// Additionally, Field supports nullable types and maps automatically between DBNull and
        /// Nullable when the generic type is nullable.
        /// </summary>
        /// <param name="row">The input DataRow</param>
        /// <param name="columnName">The input column name specifying which row value to retrieve.</param>
        /// <returns>The DataRow value for the column specified.</returns>
        public static T? Field<T>(this DataRow row, string columnName)
        {
            DataSetUtil.CheckArgumentNull(row, nameof(row));
            return UnboxT<T>.s_unbox(row[columnName]);
        }

        /// <summary>
        /// This method provides access to the values in each of the columns in a given row.
        /// This method makes casts unnecessary when accessing columns.
        /// Additionally, Field supports nullable types and maps automatically between DBNull and
        /// Nullable when the generic type is nullable.
        /// </summary>
        /// <param name="row">The input DataRow</param>
        /// <param name="column">The input DataColumn specifying which row value to retrieve.</param>
        /// <returns>The DataRow value for the column specified.</returns>
        public static T? Field<T>(this DataRow row, DataColumn column)
        {
            DataSetUtil.CheckArgumentNull(row, nameof(row));
            return UnboxT<T>.s_unbox(row[column]);
        }

        /// <summary>
        /// This method provides access to the values in each of the columns in a given row.
        /// This method makes casts unnecessary when accessing columns.
        /// Additionally, Field supports nullable types and maps automatically between DBNull and
        /// Nullable when the generic type is nullable.
        /// </summary>
        /// <param name="row">The input DataRow</param>
        /// <param name="columnIndex">The input ordinal specifying which row value to retrieve.</param>
        /// <returns>The DataRow value for the column specified.</returns>
        public static T? Field<T>(this DataRow row, int columnIndex)
        {
            DataSetUtil.CheckArgumentNull(row, nameof(row));
            return UnboxT<T>.s_unbox(row[columnIndex]);
        }

        /// <summary>
        /// This method provides access to the values in each of the columns in a given row.
        /// This method makes casts unnecessary when accessing columns.
        /// Additionally, Field supports nullable types and maps automatically between DBNull and
        /// Nullable when the generic type is nullable.
        /// </summary>
        /// <param name="row">The input DataRow</param>
        /// <param name="columnIndex">The input ordinal specifying which row value to retrieve.</param>
        /// <param name="version">The DataRow version for which row value to retrieve.</param>
        /// <returns>The DataRow value for the column specified.</returns>
        public static T? Field<T>(this DataRow row, int columnIndex, DataRowVersion version)
        {
            DataSetUtil.CheckArgumentNull(row, nameof(row));
            return UnboxT<T>.s_unbox(row[columnIndex, version]);
        }

        /// <summary>
        /// This method provides access to the values in each of the columns in a given row.
        /// This method makes casts unnecessary when accessing columns.
        /// Additionally, Field supports nullable types and maps automatically between DBNull and
        /// Nullable when the generic type is nullable.
        /// </summary>
        /// <param name="row">The input DataRow</param>
        /// <param name="columnName">The input column name specifying which row value to retrieve.</param>
        /// <param name="version">The DataRow version for which row value to retrieve.</param>
        /// <returns>The DataRow value for the column specified.</returns>
        public static T? Field<T>(this DataRow row, string columnName, DataRowVersion version)
        {
            DataSetUtil.CheckArgumentNull(row, nameof(row));
            return UnboxT<T>.s_unbox(row[columnName, version]);
        }

        /// <summary>
        /// This method provides access to the values in each of the columns in a given row.
        /// This method makes casts unnecessary when accessing columns.
        /// Additionally, Field supports nullable types and maps automatically between DBNull and
        /// Nullable when the generic type is nullable.
        /// </summary>
        /// <param name="row">The input DataRow</param>
        /// <param name="column">The input DataColumn specifying which row value to retrieve.</param>
        /// <param name="version">The DataRow version for which row value to retrieve.</param>
        /// <returns>The DataRow value for the column specified.</returns>
        public static T? Field<T>(this DataRow row, DataColumn column, DataRowVersion version)
        {
            DataSetUtil.CheckArgumentNull(row, nameof(row));
            return UnboxT<T>.s_unbox(row[column, version]);
        }

        /// <summary>
        /// This method sets a new value for the specified column for the DataRow it's called on.
        /// </summary>
        /// <param name="row">The input DataRow.</param>
        /// <param name="columnIndex">The input ordinal specifying which row value to set.</param>
        /// <param name="value">The new row value for the specified column.</param>
        public static void SetField<T>(this DataRow row, int columnIndex, T? value)
        {
            DataSetUtil.CheckArgumentNull(row, nameof(row));
            row[columnIndex] = (object?)value ?? DBNull.Value;
        }

        /// <summary>
        /// This method sets a new value for the specified column for the DataRow it's called on.
        /// </summary>
        /// <param name="row">The input DataRow.</param>
        /// <param name="columnName">The input column name specifying which row value to retrieve.</param>
        /// <param name="value">The new row value for the specified column.</param>
        public static void SetField<T>(this DataRow row, string columnName, T? value)
        {
            DataSetUtil.CheckArgumentNull(row, nameof(row));
            row[columnName] = (object?)value ?? DBNull.Value;
        }

        /// <summary>
        /// This method sets a new value for the specified column for the DataRow it's called on.
        /// </summary>
        /// <param name="row">The input DataRow.</param>
        /// <param name="column">The input DataColumn specifying which row value to retrieve.</param>
        /// <param name="value">The new row value for the specified column.</param>
        public static void SetField<T>(this DataRow row, DataColumn column, T? value)
        {
            DataSetUtil.CheckArgumentNull(row, nameof(row));
            row[column] = (object?)value ?? DBNull.Value;
        }

        private static class UnboxT<T>
        {
            internal static readonly Func<object, T?> s_unbox = Create();

            private static Func<object, T?> Create()
            {
                if (typeof(T).IsValueType && default(T) == null)
                {
                    if (!RuntimeFeature.IsDynamicCodeSupported)
                        return NullableFieldUsingReflection;

                    return CreateWhenDynamicCodeSupported();
                }
                return NonNullableField;

                [UnconditionalSuppressMessage("ReflectionAnalysis", "IL2090:MakeGenericMethod",
                    Justification = "'NullableField<TElem> where TElem : struct' implies 'TElem : new()'. Nullable does not make use of new() so it is safe." +
                    "The warning is only issued when IsDynamicCodeSupported is true.")]
                static Func<object, T?> CreateWhenDynamicCodeSupported()
                {
#pragma warning disable IL3050 // There is a path that is safe for AOT executed when IsDynamicCodeSupported is false.
                    return typeof(UnboxT<T>)
                       .GetMethod("NullableField", System.Reflection.BindingFlags.Static | System.Reflection.BindingFlags.NonPublic)!
                       .MakeGenericMethod(Nullable.GetUnderlyingType(typeof(T))!)
                       .CreateDelegate<Func<object, T>>();
#pragma warning restore IL3050 // Calling members annotated with 'RequiresDynamicCodeAttribute' may break functionality when AOT compiling.
                }
            }

            private static T? NonNullableField(object value)
            {
                if (value == DBNull.Value)
                {
                    if (default(T) is null)
                        return default;
                    throw DataSetUtil.InvalidCast(SR.Format(SR.DataSetLinq_NonNullableCast, typeof(T)));
                }
                return (T)value;
            }

            private static T? NullableFieldUsingReflection(object value)
            {
                if (value == DBNull.Value)
                    return default;

                // Try regular cast first
                if (value is T t)
                    return t;

                Type valueType = value.GetType();
                Type nullableType = Nullable.GetUnderlyingType(typeof(T))!;

                // Convert does all sorts of conversions. We are only interested in conversions for enums.
                Type fromType = valueType.IsEnum ? Enum.GetUnderlyingType(valueType) : valueType;
                Type toType = nullableType.IsEnum ? Enum.GetUnderlyingType(nullableType) : nullableType;
                if (fromType == toType)
                    value = nullableType.IsEnum ? Enum.ToObject(nullableType, value) : Convert.ChangeType(value, nullableType, null);

                return (T)value;
            }

            private static Nullable<TElem> NullableField<TElem>(object value) where TElem : struct
                => value == DBNull.Value ? default : new Nullable<TElem>((TElem)value);
        }
    }
}