C# define LET in LINQ

c#, let, linq, templates

Solution

There is an easy way to pre-compile LINQ Queries:

var distanceToFirstFromMe =
    CompiledQuery.Compile<Route, GeoCoordinates, Distance>((route, currentLocation) => {
        return route.coordinates
            .Select(c => c.position)
            .FirstOrDefault()
            .Distance(DbGeography.FromText(currentLocation, 4326));
    });

To use them in your query, you can simply call them:

IQueryable<RouteQueryModel> query =
    (from b in db.routes
     let avg_rating = b.ratings.Any() ? 
         b.ratings.Select(r => r.rating1).Average() : 0
     let distance_to_first_from_me = distanceToFirstFromMe(b, currentLocation)
     // ...

Problem

I have multiple LINQ queries that uses the same LET variables, I would like to predefine these somehow. ``` IQueryable<RouteQueryModel> query = (from b in db.routes let avg_rating = b.ratings.Any() ? b.ratings.Select(r => r.rating1).Average() : 0 let distance_to_first_from_me = b.coordinates. Select(c => c.position). FirstOrDefault(). Distance(DbGeography.FromText(currentLocation, 4326)) let distance_to_last_from_me = b.coordinates. OrderByDescending(c => c.sequence). Select(d => d.position). FirstOrDefault(). Distance(DbGeography.FromText(currentLocation, 4326)) let distance_to_from_me = distance_to_first_from_me < distance_to_last_from_me ? distance_to_first_from_me : distance_to_last_from_me where b.endpoints.Any(e => values.Any(t => t == e.town.town_id)) select new RouteQueryModel { b = b, distance_to_from_me = distance_to_from_me.Value, avg_rating = avg_rating } ); ``` I'm using those three distance_to LETs in 8 different queries, is there any way to make a template for those that i can use in my queries?

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