I've read many great answers here on stack about dynamic creation of lambda expression, but cannot make my own.
I need to select entity from DB by ID
, but I don't know its type beforehand. Only name of a type. So:
var modelType = Assembly.Load("Models").GetTypes().First(t => t.Name == type + "Model");
MethodInfo method = typeof(CommonRepository).GetMethod("GetByExpression",
BindingFlags.Instance | BindingFlags.Public);
var arg = Expression.Constant(null, modelType);
var body = Expression.Convert(Expression.PropertyOrField(arg, "ID"),
typeof(int));
var lambda = Expression.Lambda<Func<object, bool>>(body);
var model = method.Invoke(this, new object[] { lambda });
var field = modelType.GetProperty("Disable", BindingFlags.Instance);
field.SetValue(model, false);
this.marathonRepository.SaveOrUpdate(model);
I guess in my code I've made "e.ID
" part of lambda. How to make "== id
" part?
I try to break the expression up into its parts, using comments to help understand the expression to be built.
Consider the following...
// id
var id = 2;
var idConstant = Expression.Constant(id);
// (object e) => ...
var param = Expression.Parameter(typeof(object));
// (object e) => ((modelType)e).ID
var property = Expression.PropertyOrField(Expression.Convert(param, modelType), "ID"));
// (object e) => ((modelType)e).ID == id
var body = Expression.Equal(property, idConstant);
var lambda = Expression.Lambda<Func<object, bool>>(body, param);