Why are some properties of the UnaryExpression object and other MemberExpression?

Question

Fulfilling the answer to mine, select the model property using the lambda name rather than the string property name , wanting to add the properties to the collection as follows:

var props = new ExportPropertyInfoCollection<JobCard>(); props.Include(model => model.BusinessInstallNumber).Title("Install No").Width(64).KeepZeroPadding(true); props.Include(model => model.DeviceName).Title("Device").Width(70); props.Include(model => model.DateRequested).Title("Request Date").Format("{0:dd/MM/yyyy}").Width(83); 

I wrote the following code in the Include method:

 public class PropertyCollection<T> { public void Include(Expression<Func<T, object>> expression) { var memberExpression = expression.Body as MemberExpression; if (memberExpression != null) { var pes = new ExportPropertyInfoBuilder {Property = new ExportPropertyInfo {Property = memberExpression.Member as PropertyInfo}}; Properties.Add(pes.Property.Property.Name, pes.Property); return pes; } 

However, when I ran the code, I found that some of the lambdas gave MemberExpression values ​​as expected, but others gave UnaryExpression values. I had to change the first line of code to the following before I could add all my properties using lambdas:

 var memberExpression = expression.Body as MemberExpression ?? ((UnaryExpression) expression.Body).Operand as MemberExpression; 

All properties are "simple", i.e. string, DateTime, int, bool, etc. in the POCO business object. They are decorated with several changing attributes of DataAnnotations .

What makes some of the lambdas in my example get MemberExpression values ​​and other UnaryExpression values? In my example, the first UnaryExpression is on the third line, the DateTime property, but the boolean properties also lead to UnaryExpressionions .

Answer 1

I think I know what the problem is. Your expression returns the type object .

If you change this to Expression<Func<T, R>> , the return type must be correctly inferred, and UnaryExpression (which I assume is some kind of boxing operation) should not occur.

Update:

The signature for Include must be:

 public void Include<T, R>(Expression<Func<T, R>> expression)