title: go-pg got doesn't has relation thought on my table has relation
body: <p>i have a contacts relation to provinces, and here is on my struct</p>
  <pre><code>    Contact struct {
          tableName       struct{}    `pg:&quot;contacts,discard_unknown_columns&quot;`
          ID              int         `json:&quot;id&quot;`
          Address         string      `json:&quot;address&quot;`
          BuildingType    string      `json:&quot;building_type&quot;`
          BuildingNumber  float64     `json:&quot;building_number&quot;`
          Province        *Province   `pg:&quot;fk:province_id&quot; json:&quot;province&quot;`
      }
  
      Province struct {
          tableName      struct{}         `pg:&quot;provinces,discard_unknown_columns&quot;`
          ID             int              `json:&quot;id&quot; pg:&quot;,pk&quot;`
          Name           string           `json:&quot;name&quot;`
      }
  </code></pre>
  <p>and here how i call:</p>
  <pre><code>    var us Contact
      err = db.Model(&amp;us).Relation(&quot;provinces&quot;).Where(
          &quot;id = ?&quot;, 3,
      ).Select()
  </code></pre>
  <p>what i go is <code> model=Contact does not have relation=&quot;provinces&quot;</code>
  how to correct way to query this with go-pg?</p>
  <p>when i change tag on Contact for Province with tag <code>pg:&quot;rel:has-one&quot;</code></p>
  <p>i got this error
  <code>pg: Contact has-one Province: Contact must have column province_id (use fk:custom_column tag on Province field to specify custom column)</code></p>
  <p>note: i dont use their migration, i use sql-migration for all migrations</p>