Linq To Xml Null Checking of attributes

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面向向阳花
面向向阳花 2021-02-20 18:39

   
   
   

        
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  • 2021-02-20 19:25

    In C# 6.0 you can use monadic Null-conditional operator ?. After applying it in your example it would look like this:

    var books = from book in booksXml.Descendants("book")
                select new
                {
                    Name = book.Attribute("name")?.Value ?? String.Empty,
                    Price = Convert.ToInt32(book.Attribute("price")?.Value ?? "0"),
                    Special = book.Attribute("special")?.Value ?? String.Empty
                };
    

    You can read more here in part titled Null-conditional operators.

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  • 2021-02-20 19:30

    How about using an extension method to encapsulate the missing attribute cases:

    public static class XmlExtensions
    {
        public static T AttributeValueOrDefault<T>(this XElement element, string attributeName, T defaultValue)
        {
            var attribute = element.Attribute(attributeName);
            if (attribute != null && attribute.Value != null)
            {
                return (T)Convert.ChangeType(attribute.Value, typeof(T));
            }
    
            return defaultValue;
        }
    }
    

    Note that this will only work if T is a type to which string knows to convert via IConvertible. If you wanted to support more general conversion cases, you may need to look for a TypeConverter, as well. This will throw an exception if the type fails to convert. If you want those cases to return the default as well, you'll need to perform additional error handling.

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  • 2021-02-20 19:40

    You can cast the attribute to a string. If it is absent you will get null and subsequent code should check for null, otherwise it will return the value directly.

    Try this instead:

    var books = from book in booksXml.Descendants("book")
                select new
                {
                    Name = (string)book.Attribute("name"),
                    Price = (string)book.Attribute("price"),
                    Special = (string)book.Attribute("special")
                };
    
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