Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1263514
Description of problem:
When dissociating a host from a compute resource and then deleting a compute profile/resource it leaves behind the compute_resource_id and compute_profile_id in the hosts table causing a FK error in postgres upon adding/editing the compute_resource and compute profile page

Version-Release number of selected component (if applicable):
6.0/6.1

How reproducible:

Steps to Reproduce:
1. install sat 6.0/6.1 setup compute resource/profile
2. build host with compute profile/resource
3. delete compute profile/resource
4. try to add/modify compute resource/profile

Actual results:

PGError
ERROR: update or delete on table "compute_profiles" violates foreign key constraint "hosts_compute_profile_id_fk" on table "hosts" DETAIL: Key (id)=(9) is still referenced from table "hosts".
app/controllers/compute_profiles_controller.rb:37:in `destroy'
app/models/concerns/foreman/thread_session.rb:33:in `clear_thread'
lib/middleware/catch_json_parse_errors.rb:9:in `call'

PGError
ERROR: update or delete on table "compute_resources" violates foreign key constraint "hosts_compute_resource_id_fk" on table "hosts" DETAIL: Key (id)=(3) is still referenced from table "hosts".
app/controllers/compute_resources_controller.rb:68:in `destroy'
app/models/concerns/foreman/thread_session.rb:33:in `clear_thread'
lib/middleware/catch_json_parse_errors.rb:9:in `call'

Expected results:
a cascade delete setting the id fields in the hosts table for compute resource/profile to ""/nil

Additional info:

Steps I used to do a work-around:

We are changing to our auth user:
irb(main):001:0> User.current = User.first
2015-08-29 17:15:30 [D] User Load (0.3ms) SELECT "users".* FROM "users" ORDER BY firstname LIMIT 1
=> #<User id: 3, login: "hbcdigital", firstname: "Admin", lastname: "User", mail: "hbcdigitalunix@saksinc.com", admin: true, last_login_on: "2015-08-26 19:54:31", auth_source_id: 1, created_at: "2015-04-28 20:31:32", updated_at: "2015-08-26 19:54:31", password_hash: "966ce2a137f20279ac685b3ac66e156c2d57a341", password_salt: "ebe67ddf59d3fd59f6c0be17828f6b7e12db7bb6", locale: nil, helptips_enabled: true, page_size: 25, disabled: false, preferences: #<struct ActiveRecord::AttributeMethods::Serialization::Attribute coder=#<ActiveRecord::Coders::YAMLColumn:0x000000093d1bd0 @object_class=Hash>, value="---\n:dashboard:\n errata:\n :page_size: 30\n", state=:serialized>, remote_id: "hbcdigital-1a03a276", avatar_hash: nil, default_organization_id: 1, default_location_id: 2, lower_login: "hbcdigital", mail_enabled: true>

I am selecting the host based on the id of the systems that are coming back from my query in postgresql and making it a variable

irb(main):002:0> host = Host.find(44)
2015-08-29 17:15:42 [D] Host::Managed Load (1.4ms) SELECT "hosts".* FROM "hosts" WHERE "hosts"."type" IN ('Host::Managed') AND "hosts"."id" = $1 LIMIT 1 "id", 44
=> #<Host::Managed id: 44, name: "hd3qoms08lx.digital.hbc.com", ip: "10.130.216.78", last_compile: nil, last_freshcheck: nil, last_report: nil, updated_at: "2015-07-31 15:34:35", source_file_id: nil, created_at: "2015-06-02 14:10:20", mac: "00:50:56:9f:4d:b7", root_pass: "$1$FzxLojwn$AFFJeSM4iKaRq5DA4QuaU1", serial: nil, puppet_status: 0, domain_id: 1, architecture_id: 1, operatingsystem_id: 4, environment_id: 1, subnet_id: 2, ptable_id: 14, medium_id: 7, build: false, comment: "", disk: "", installed_at: "2015-06-02 14:23:11", model_id: nil, hostgroup_id: nil, owner_id: 3, owner_type: "User", enabled: true, puppet_ca_proxy_id: 1, managed: true, use_image: nil, image_file: nil, uuid: "501fa5c1-f9f1-e50f-ee04-7b93a99107d2", compute_resource_id: 3, puppet_proxy_id: 1, certname: nil, image_id: nil, organization_id: 1, location_id: 3, type: "Host::Managed", otp: nil, realm_id: nil, compute_profile_id: nil, provision_method: "build", content_source_id: 1, primary_interface: nil, grub_pass: "", discovery_rule_id: nil, content_view_id: nil, lifecycle_environment_id: nil>
irb(main):003:0> host.compute_resource_id = "nil"

I am editing the compute resource to nil

irb(main):003:0> host.compute_resource_id = ""

Now to save my changes:

irb(main):011:0> host.save