在AssignmentExpression中使用的MethodCallExpression返回默认值

我正在为我的公司开发一个简单的ORM，并使用反射从查询到目前为止自动填充属性。这显然是相当慢的，我想用表达式树来提高性能。我花了大量的时间跟随示例并阅读适当的调用，现在我的代码编译并执行了!然而，我有一个MethodCallExpression执行基本的DBNull检查和类似的似乎工作正常，但是当值被分配给属性时，它发送类型的默认值。

首先是实际代码:

    public static void PopulateFromReaderUsingExpression(Descriptor descriptor, IDataRecord reader)
    {
        if (descriptor == null)
            throw new ArgumentNullException("descriptor");
        if (reader == null)
            throw new ArgumentNullException("reader");
        string[] AvailableColumnsInReader = new string[reader.FieldCount];
        for (int i = 0; i <= reader.FieldCount - 1; i++)
        {
            AvailableColumnsInReader[i] = reader.GetName(i).ToUpper(CultureInfo.InvariantCulture);
        }
        var statements = new List<Expression>();
        ParameterExpression readerExp = Expression.Parameter(typeof(IDataRecord));
        ParameterExpression descriptorExp = Expression.Variable(descriptor.GetDescriptorType(), "descriptor");
        BinaryExpression createInstanceExp = Expression.Assign(
            descriptorExp, Expression.New(descriptor.GetDescriptorType()));
        statements.Add(createInstanceExp);
        foreach (KeyValuePair<PropertyInfo, PropertyMapping> pair in descriptor.ReadablePropertiesAndDataNames
            .Where(property => AvailableColumnsInReader.Contains(property.Value.ReturnName.ToUpper(CultureInfo.InvariantCulture))))
        {
            MemberExpression propertyExp = Expression.Property(descriptorExp, pair.Key);
            IndexExpression readValue =
                Expression.MakeIndex(readerExp, typeof(IDataRecord).GetProperty("Item", new[] { typeof(string) }),
                new[] { Expression.Constant(pair.Value.ReturnName) });
            MethodCallExpression castValueExp =
                Expression.Call(typeof(Descriptor)
                    .GetMethod("CastValue",
                        BindingFlags.Static | BindingFlags.Public,
                        null,
                        new Type[]
                        {
                            typeof(Type), typeof(object), typeof(object)
                        },
                        null), Expression.Constant(pair.Key.PropertyType, typeof(Type)), readValue, Expression.Constant(null));
            BinaryExpression assignmentExp = Expression.Assign(propertyExp, Expression.Convert(castValueExp, pair.Key.PropertyType));
            statements.Add(assignmentExp);
        }
        var body = Expression.Block(new ParameterExpression[] { descriptorExp }, statements);
        Expression.Lambda<Action<IDataRecord>>(body, readerExp).Compile()(reader);
    }

正在被MethodCallExpression及其重载调用的方法:

    /// <summary>
    /// Detects if a value is DBNull, null, or has value.
    /// </summary>
    /// <param name="newType">The new type.</param>
    /// <param name="value">The value.</param>
    /// <param name="defaultValue">The default value.</param>
    /// <param name="typeName">Name of the type from the database (used for date/time to string conversion).</param>
    /// <returns>Value as type T if value is not DBNull, null, or invalid cast; otherwise defaultValue.</returns>
    public static object CastValue(Type newType, object value, object defaultValue, string typeName)
    {
        object returnValue;
        if (value is DBNull || value == null)
            returnValue = defaultValue;
        else if (newType == typeof(bool) && (value.GetType() == typeof(Int16) || value.GetType() == typeof(Int32)))
            returnValue = ((object)(int.Parse(value.ToString(), CultureInfo.InvariantCulture) > 0 ? true : false));
        else if (newType == typeof(int) && value.GetType() == typeof(long))
            returnValue = ((object)((int)((long)value)));
        else if (newType == typeof(int) && value.GetType() == typeof(decimal))
            returnValue = ((object)((int)((decimal)value)));
        else if (newType == typeof(string))
        {
            returnValue = value.ToString();
            if (!string.IsNullOrEmpty(typeName))
                if (typeName == "date")
                    returnValue = ((DateTime)value).ToString("MM/dd/yyyy", CultureInfo.CurrentCulture);
        }
        else
            returnValue = value;
        return returnValue;
    }
    /// <summary>
    /// Casts the value.
    /// </summary>
    /// <param name="newType">The new type.</param>
    /// <param name="value">The value.</param>
    /// <param name="defaultValue">The default value.</param>
    /// <returns>System.Object.</returns>
    public static object CastValue(Type newType, object value, object defaultValue)
    {
        return CastValue(newType, value, defaultValue, null);
    }

我已经确认值正在进入方法并返回，但是在此过程中丢失了，我的猜测是在赋值操作中。

这里我将包括代码示例中使用的相关方法签名:

public virtual Dictionary<PropertyInfo, PropertyMapping> ReadablePropertiesAndDataNames
/// <summary>
/// THe object Orochi CRUDE uses to map properties to database actions.
/// </summary>
public class PropertyMapping
{
    /// <summary>
    /// Initializes a new instance of the <see cref="PropertyMapping" /> class.
    /// </summary>
    /// <param name="property">The property.</param>
    /// <param name="parameterName">Name of the parameter.</param>
    /// <param name="returnName">Name of the return.</param>
    /// <exception cref="System.ArgumentNullException">property</exception>
    public PropertyMapping(PropertyInfo property, string returnName)
    {
        if (property == null)
            throw new ArgumentNullException("property");
        Contract.EndContractBlock();
        this.ReturnName = !string.IsNullOrWhiteSpace(returnName) ? returnName : property.Name;
    }
    /// <summary>
    /// Gets the name of the return.
    /// </summary>
    /// <value>
    /// The name of the return.
    /// </value>
    public string ReturnName { get; private set; }
}

这是我的语句块中的DebugInfo:

.Block(Models.Billing.Claims.BillingQueue $descriptor) {
    $descriptor = .New Models.Billing.Claims.BillingQueue();
    $descriptor.ClaimWorkQueueId = (System.Int32).Call Orochi.CrudeData.Descriptor.CastValue(
        .Constant<System.Type>(System.Int32),
        $var1.Item["ClaimWorkQueueId"],
        null);
    $descriptor.WorkQueueName = (System.String).Call Orochi.CrudeData.Descriptor.CastValue(
        .Constant<System.Type>(System.String),
        $var1.Item["WorkQueueName"],
        null);
    $descriptor.Count = (System.Int32).Call Orochi.CrudeData.Descriptor.CastValue(
        .Constant<System.Type>(System.Int32),
        $var1.Item["ClaimCount"],
        null)
}

/// <summary>
/// Builds the mapping expression.
/// </summary>
/// <param name="descriptor">The descriptor.</param>
/// <param name="reader">The reader.</param>
/// <returns>LambdaExpression.</returns>
public static Expression<Func<IDataRecord, object>> BuildMappingExpression(IDescriptor descriptor, IDataRecord reader, string[] availableColumns)
{
    var statements = new List<Expression>();
    ParameterExpression readerExp = Expression.Parameter(typeof(IDataRecord));
    ParameterExpression descriptorExp = Expression.Variable(descriptor.GetDescriptorType(), "descriptor");
    BinaryExpression createInstanceExp = Expression.Assign(
        descriptorExp, Expression.New(descriptor.GetDescriptorType()));
    statements.Add(createInstanceExp);
    foreach (KeyValuePair<PropertyInfo, PropertyMapping> pair in descriptor.ReadablePropertiesAndDataNames
        .Where(property => availableColumns.Contains(property.Value.ReturnName.ToUpper(CultureInfo.InvariantCulture))))
    {
        MemberExpression propertyExp = Expression.Property(descriptorExp, pair.Key);
        IndexExpression readValue =
            Expression.MakeIndex(readerExp, typeof(IDataRecord).GetProperty("Item", new[] { typeof(string) }),
            new[] { Expression.Constant(pair.Value.ReturnName) });
        MethodCallExpression castValueExp =
            Expression.Call(typeof(Descriptor)
                .GetMethod("CastValue",
                    BindingFlags.Static | BindingFlags.Public,
                    null,
                    new Type[]
                    {
                        typeof(Type), typeof(object), typeof(object)
                    },
                    null), Expression.Constant(pair.Key.PropertyType, typeof(Type)), readValue, Expression.Constant(null));
        BinaryExpression assignmentExp = Expression.Assign(propertyExp, Expression.Convert(castValueExp, pair.Key.PropertyType));
        statements.Add(assignmentExp);
    }
    statements.Add(descriptorExp);
    var body = Expression.Block(new ParameterExpression[] { descriptorExp }, statements);
    return Expression.Lambda<Func<IDataRecord, object>>(body, readerExp);
}