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Optimizing Expressions

EQL has a global BeforeExecuting hook on ExecutionOptions allowing you to intercept expressions before they are executed and modify them. Linq.Expression.Optimizer contains an expression tree visitor allowing you to simply:

  var options = new EntityGraphQL.Schema.ExecutionOptions();
  options.BeforeExecuting += (expression, isFinal) =>
  {
      // isFinal == true if the expression is the final execution - this means
      //  - ExecuteServiceFieldsSeparately = false, or
      //  - The query does not reference any fields with services
      //  - The query references fields with service and the first execution has completed (isFinal == false) and we are executing again to merge the service results
      return ExpressionOptimizer.visit(expression);
  };

Linq Optimizer appears to use expression methods on IEnumerable<T> which isn't directly compatible with this approach (there are expression trees in the project so it may work if you can use a lower level api call), you would need to test that the return type of expression is compatible.