Storing decimal data type in Azure Tables

Question

Windows Azure Table Storage does not support the decimal data type.

A suggested workaround is to use a custom attribute to serialize the decimal property as string:

[EntityDataType(PrimitiveTypeKind.String)]
public decimal Quantity { get; set; }

How could this EntityDataType custom attribute be implemented so decimal properties can be stored and retrieved from Windows Azure Tables?

Answer 1

Overriding ReadEntity and WriteEntity in the base class is good for this. It's not necessary to write an EntityResolver every time you retrieve the entities.

public class CustomTableEntity : TableEntity
{
    public override void ReadEntity(IDictionary<string, EntityProperty> properties, OperationContext operationContext)
    {
        base.ReadEntity(properties, operationContext);

        foreach (var thisProperty in
            GetType().GetProperties().Where(thisProperty =>
                thisProperty.GetType() != typeof(string) &&
                properties.ContainsKey(thisProperty.Name) &&
                properties[thisProperty.Name].PropertyType == EdmType.String))
        {
            var parse = thisProperty.PropertyType.GetMethods().SingleOrDefault(m =>
                m.Name == "Parse" &&
                m.GetParameters().Length == 1 &&
                m.GetParameters()[0].ParameterType == typeof(string));

            var value = parse != null ?
                parse.Invoke(thisProperty, new object[] { properties[thisProperty.Name].StringValue }) :
                Convert.ChangeType(properties[thisProperty.Name].PropertyAsObject, thisProperty.PropertyType);

            thisProperty.SetValue(this, value);
        }
    }

    public override IDictionary<string, EntityProperty> WriteEntity(OperationContext operationContext)
    {
        var properties = base.WriteEntity(operationContext);

        foreach (var thisProperty in
            GetType().GetProperties().Where(thisProperty =>
                !properties.ContainsKey(thisProperty.Name) &&
                typeof(TableEntity).GetProperties().All(p => p.Name != thisProperty.Name)))
        {
            var value = thisProperty.GetValue(this);
            if (value != null)
            {
                properties.Add(thisProperty.Name, new EntityProperty(value.ToString()));
            }
        }

        return properties;
    }
}

When you use, just make your entities extend from CustomTableEntity and it will be transparent when inserting or retrieving entities. It supports DateTime, TimeSpan, decimal and those types who have Parse method or implement IConvertible interfaces.