address - Page 254 - Developer IT

Get the property, as a string, from an Expression<Func<TModel,TProperty>>

- by Jaxidian

I use some strongly-typed expressions that get serialized to allow my UI code to have strongly-typed sorting and searching expressions. These are of type Expression<Func<TModel,TProperty>> and are used as such: SortOption.Field = (p => p.FirstName);. I've gotten this working perfectly for this simple case. The code that I'm using for parsing the "FirstName" property out of there is actually reusing some existing functionality in a third-party product that we use and it works great, until we start working with deeply-nested properties(SortOption.Field = (p => p.Address.State.Abbreviation);). This code has some very different assumptions in the need to support deeply-nested properties. As for what this code does, I don't really understand it and rather than changing that code, I figured I should just write from scratch this functionality. However, I don't know of a good way to do this. I suspect we can do something better than doing a ToString() and performing string parsing. So what's a good way to do this to handle the trivial and deeply-nested cases? Requirements: Given the expression p => p.FirstName I need a string of "FirstName". Given the expression p => p.Address.State.Abbreviation I need a string of "Address.State.Abbreviation" While it's not important for an answer to my question, I suspect my serialization/deserialization code could be useful to somebody else who finds this question in the future, so it is below. Again, this code is not important to the question - I just thought it might help somebody. Note that DynamicExpression.ParseLambda comes from the Dynamic LINQ stuff and Property.PropertyToString() is what this question is about. /// <summary> /// This defines a framework to pass, across serialized tiers, sorting logic to be performed. /// </summary> /// <typeparam name="TModel">This is the object type that you are filtering.</typeparam> /// <typeparam name="TProperty">This is the property on the object that you are filtering.</typeparam> [Serializable] public class SortOption<TModel, TProperty> : ISerializable where TModel : class { /// <summary> /// Convenience constructor. /// </summary> /// <param name="property">The property to sort.</param> /// <param name="isAscending">Indicates if the sorting should be ascending or descending</param> /// <param name="priority">Indicates the sorting priority where 0 is a higher priority than 10.</param> public SortOption(Expression<Func<TModel, TProperty>> property, bool isAscending = true, int priority = 0) { Property = property; IsAscending = isAscending; Priority = priority; } /// <summary> /// Default Constructor. /// </summary> public SortOption() : this(null) { } /// <summary> /// This is the field on the object to filter. /// </summary> public Expression<Func<TModel, TProperty>> Property { get; set; } /// <summary> /// This indicates if the sorting should be ascending or descending. /// </summary> public bool IsAscending { get; set; } /// <summary> /// This indicates the sorting priority where 0 is a higher priority than 10. /// </summary> public int Priority { get; set; } #region Implementation of ISerializable /// <summary> /// This is the constructor called when deserializing a SortOption. /// </summary> protected SortOption(SerializationInfo info, StreamingContext context) { IsAscending = info.GetBoolean("IsAscending"); Priority = info.GetInt32("Priority"); // We just persisted this by the PropertyName. So let's rebuild the Lambda Expression from that. Property = DynamicExpression.ParseLambda<TModel, TProperty>(info.GetString("Property"), default(TModel), default(TProperty)); } /// <summary> /// Populates a <see cref="T:System.Runtime.Serialization.SerializationInfo"/> with the data needed to serialize the target object. /// </summary> /// <param name="info">The <see cref="T:System.Runtime.Serialization.SerializationInfo"/> to populate with data. </param> /// <param name="context">The destination (see <see cref="T:System.Runtime.Serialization.StreamingContext"/>) for this serialization. </param> public void GetObjectData(SerializationInfo info, StreamingContext context) { // Just stick the property name in there. We'll rebuild the expression based on that on the other end. info.AddValue("Property", Property.PropertyToString()); info.AddValue("IsAscending", IsAscending); info.AddValue("Priority", Priority); } #endregion }

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