What is the correct syntax for RavenDB Search method in F#

Question

I am trying to find all posts in RavenDB containing a word (index is there)

Here is a query that works, finds everything that starts with 'Liv'

let post = query {
    for post in session.Query<MyType>() do
    where (post.Text.StartsWith("Liv"))
    select post
}

An attempt to use string.Contains() method as condition of Where closure, will throw NotSupportedException. Here

So I am trying to use Search method where:

Expression<Func<T, object>> fieldSelector, 
// Expression marking a field in which terms should be looked for.

C# equivalent from docs:

List<User> users = session
    .Query<User>("Users/ByNameAndHobbies")
    .Search(x => x.Name, "Adam")
    .Search(x => x.Hobbies, "sport")
    .ToList();

My first try was to go with

let x = session.Query<MyType>(index).Search((fun xe -> xe.Text ), "Liv")

But getting error because it expects object out. Tried to downcast String to Object (what a strange idea), but getting:

Cannot understand how to translate x => x.Invoke(xe)

At the moment, I am out of ideas. I am supposed to mark field for search and return object. Any ideas?

Thank you.

EDIT 1: My expression. Gets runtime InvalidCastException because it can't cast string to obj.

let expr = 
  <@ Func<MyType, _>(fun xe -> xe.Text ) @>
  |> LeafExpressionConverter.QuotationToExpression 
  |> unbox<System.Linq.Expressions.Expression<Func<MyType, _>>>

Answer 1

You mentioned that you tried casting the string to object. I tried it using :> obj and it does work.

Here is my working query:

let expr = <@ Func<MyType,_>(fun x -> x.Text :> obj ) @>
                |> LeafExpressionConverter.QuotationToExpression
                |> unbox<Linq.Expressions.Expression<Func<MyType,_>>>
let events = session.Query<MyType>()
                .Search(expr, "Liv*", decimal 1, SearchOptions.Or, EscapeQueryOptions.AllowAllWildcards)
                |> List.ofSeq