Angular JS Service DI from another module

Question

I am running into an issue injecting a service from an angular js module into my main controller. I am getting this error: https://docs.angularjs.org/error/$injector/unpr?p0=aProvider%20%3C-%20a%20%3C-%20solrquery

My code is below:

var app = angular.module('app1',[
    'solr'
    ]);

app.controller('app1cont', ['$scope', 'solrquery', function($scope,solrquery){
    console.log("Start");
    $scope.value = 1;
    solrquery('aaa');

}]);

The solr module looks like this:

var solr1 = angular.module('solr', []);

solr1.run(function(){
    console.log("Module Loaded");
});

solr1.service('solrquery',function(a) {
    console.log('searching for: ' + a);
}
);

When I run it, I see Module Loaded printed to the console and an error. If I remove the injection from the app.controller and solrquery('aaa'); the code runs fine... Spent several hours on this already, any help would be much appreciated.

Thanks in advance.

EDIT:

Thanks to Anthony for the answer, after re-working the code, the module looks like this:

var solr1 = angular.module('solr', []);

solr1.run(function(){
    console.log("Module Loaded");
});
//as a factory
solr1.factory('solrquery',function() {
    return function(a) {
        console.log('searching for: ' + a);
    }
}
);
//as a service
solr1.service('solrser', function() { 
    this.test = function(a) {
        console.log(a);
    }
});

And the controller: var app = angular.module('app1',[ 'solr' ]);

app.controller('app1cont', ['$scope', 'solrquery', 'solrser', function($scope,solrquery,solrser){
    console.log("Start");
    $scope.value = 1;
    solrquery('a');
    solrser.test('a');

}]);

Answer 1

The injector is complaining because it is looking for something called a to inject into the service. You can fix this by changing solrquery to a factory that returns a function...

solr1.factory('solrquery', function () {
    return function (a) {
        console.log('searching for: ' + a);
    };
});

Live Demo

Note that leaving it as a service technically still works, but a function that returns something should really be a factory.

Answer 2

That angularjs.org error link tells you what the problem is.

Unknown provider: aProvider <- a <- solrquery

Angular's injector is looking for a dependency called a which is specified in the function parameters for the solrquery service:

solr1.service('solrquery',function(a) {

Your service definition needs to be reworked. This is a good reference for how you should be defining services: angular.service vs angular.factory.