on $search => isearchbinder_notasync => querybindercontext.arbitraryentity

[vigouredelaruse]

given: a generic<,> single odata controller per edm with associated icontrollermodelconvention and all the trimmings

problem statement:

• $search and isearchbinder.bindsearch() imply special expression tree ops when not all edm entities are known at compile time
• there is no opportunity to use a static Func<T, bool>blah => predicate or other predicate if not this predicate
• public Expression BindSearch() implies selecting properties for comparison expressions from context.ElementClrType or compile time evaluation of p => p.knownproperty.contains(searchterm)

i'm telling you this because my ai assistants don't know enough about this pattern to refactor it such that entity.propertyset can be expressed as an array, and google copilot has no examples of the associated expression tree rendering

so here you go.

this example supports $search on a well known set of interface properties by trying get ef core to render sql like for a set of entities not known at compile time

       private Expression GetDefaultSearchExpression(Type t, string value)
       {
           var parameter = Expression.Parameter(t, "e");
           var constantExpr = Expression.Constant(value);
           var displayNameProperty = t.GetProperty(nameof(IContentRowLevelSecured.DisplayName), BindingFlags.Public | BindingFlags.Instance);
           var descriptionProperty = t.GetProperty(nameof(IContentRowLevelSecured.Description), BindingFlags.Public | BindingFlags.Instance);
           var dictionaryKeyProperty = t.GetProperty(nameof(IContentRowLevelSecured.DictionaryKey), BindingFlags.Public | BindingFlags.Instance);

           MemberExpression displayNameMemberExpression = GetMemberExpressionForProperty(parameter, displayNameProperty);
           MemberExpression descriptionMemberExpression = GetMemberExpressionForProperty(parameter, descriptionProperty);
           MemberExpression dictionaryKeyMemberExpression = GetMemberExpressionForProperty(parameter, dictionaryKeyProperty);


           // https://stackoverflow.com/questions/73570842/not-like-in-ef-core-expression-tree
           var displayNameQuery = Expression.Call(typeof(DbFunctionsExtensions), "Like", 
                               Type.EmptyTypes, Expression.Constant(EF.Functions), displayNameMemberExpression, constantExpr);
           var descriptionQuery = Expression.Call(typeof(DbFunctionsExtensions), "Like", 
                               Type.EmptyTypes, Expression.Constant(EF.Functions), descriptionMemberExpression, constantExpr);
           var dictionaryKeyQuery = Expression.Call(typeof(DbFunctionsExtensions), "Like", 
                           Type.EmptyTypes, Expression.Constant(EF.Functions), dictionaryKeyMemberExpression, constantExpr);

           var predicate = Expression.OrElse(displayNameQuery, descriptionQuery);
           predicate = Expression.OrElse(predicate, dictionaryKeyQuery);

           // create the return value by reflection
           var lambdaType = typeof(Func<,>).MakeGenericType(t, typeof(bool));
           var lambda = Expression.Lambda(lambdaType, predicate, parameter);
           return lambda;

       }

invoke this from

public class YourSemiAutonomousSearchBinder:  ISearchBinder{
 
        public Expression BindSearch(SearchClause searchClause, QueryBinderContext context){
            SearchTermNode node = searchClause.Expression as SearchTermNode;
            var searchTerm = node.Text;

            // you could  extend this if statement for every type and property set in your edm
            if (context.ElementClrType == typeof(MyTypeContainsDisplayNameAndDescription))
            {
                // check the displayname

                Expression<Func<MyTypeContainsDisplayNameAndDescription, bool>> exp = p =>
                (p.DisplayName.Contains(searchTerm)
                || p.Description.Contains(searchTerm);
                return exp;
            }

          // or you could generalize the property sets in an interface implemented by entities in the edm
          // and dynamically render the predicates and return expression
          return GetDefaultSearchExpression(context.ElementClrType, searchTerm);
      }
}