title: Redux Selector not called
body: <p>I have the following situation:</p>
  
  <p>A selector for a list of countries in my app state</p>
  
  <pre><code>export const getCountries = state =&gt; state.countries;
  </code></pre>
  
  <p>And a selector created using reselect to filter for a country with a specific id</p>
  
  <pre><code>export const getCountryById = countryId =&gt; 
      createSelector(
          [getCountries],
          (countries) =&gt; {
              let countriesList = countries.filter(c =&gt; c.id === countryId);
              if ( countriesList ) {
                  return countriesList[0];
              }
              return null;
          }
      )
  </code></pre>
  
  <p>Then a have a country details page component ( acessed through <a href="http://localhost:3000/country/4" rel="nofollow noreferrer">http://localhost:3000/country/4</a> )</p>
  
  <pre><code>import React from 'react';
  import { getCountryById } from '../redux/selectors';
  import { connect } from 'react-redux';
  
  const CountryPage = ({country}) =&gt; {
      return &lt;h1&gt;{country.name}&lt;/h1&gt;
  }
  
  const mapStateToProps = (state, ownProps) =&gt; {
      console.log(ownProps.match.params.countryId);
      const obj = {
          country: getCountryById(ownProps.match.params.countryId)
      }
      return obj;
  };
  
  export default connect(mapStateToProps, null)(CountryPage);
  </code></pre>
  
  <p>The mapStateToProps is correctly receiving the countryId, but the selector is not being called. What am I missing here ? </p>
  
  <p>Or is it the wrong approach to using the selectors ? I am aware that I can use the full country list from state in the CountryPage and filter it there, but what is the best practice here ?</p>