Null columns are created on either tables when accessing data using Spring Data JPA
<p>I am new to Spring Data JPA and Hibernate. By looking at different examples I built a working model for CRUD operations on one entity, I am having trouble in joining two tables to extract AF_NAME using AF_ID from another table which is Foreign key. A null column is created with the names of and while accessing, null is returned.please check if I am following preocedure for joins and point me to any tutorial know. 
  <a href="https://stackoverflow.com/questions/19977130/joining-two-table-entities-in-spring-data-jpa">I followed this solution and still there is no progress.</a></p>

<pre><code>@Entity
@Configuration
@EnableAutoConfiguration
@Table(name = "AFF_CONFIG")
public class AFF_CONFIG implements Serializable {

@Id
@Column(name = "AFF_CONFIG_ID")
private String AFF_CONFIG_ID;

@Column(name = "AFF_ID")
private String AFF_ID;

@Column(name = "CH_ID")
private String CH_ID;

@Column(name = "M_ID")
private Long M_ID;

@Column(name = "KEY")
private String KEY;

@Column(name = "VALUE")
private String VALUE;

@Column(name = "SYSTEM")
private String SYSTEM;

private AFF aff;

@LazyCollection(LazyCollectionOption.TRUE)
@ManyToOne
@JoinColumn(name = "AFF_ID")
public AFF getAff() {
    return aff;
}

public void setAffiliate(AFF aff) {
    this.aff = aff;
}

public String getAFF_CONFIG_ID() {
    return AFF_CONFIG_ID;
}

public void setAFF_CONFIG_ID(String aFF_CONFIG_ID) {
    AFF_CONFIG_ID = aFF_CONFIG_ID;
}

public String getAFF_ID() {
    return AFF_ID;
}

public void setAFF_ID(String aFF_ID) {
    AFF_ID = AFF_ID;
}

public String getCH_ID() {
    return CH_ID;
}

public void setCHANNEL_ID(String cH_ID) {
    CH_ID = cH_ID;
}

public Long getM_ID() {
    return M_ID;
}

public void setM_ID(Long m_ID) {
    M_ID = m_ID;
}

public String getKEY() {
    return KEY;
}

public void setKEY(String kEY) {
    KEY = kEY;
}

public String getVALUE() {
    return VALUE;
}

public void setVALUE(String vALUE) {
    VALUE = vALUE;
}

public String getSYSTEM() {
    return SYSTEM;
}

public void setSYSTEM(String sYSTEM) {
    SYSTEM = sYSTEM;
}
</code></pre>

<p>Second entity is:</p>

<pre><code>@Entity
@Table(name = "AFF")
public class AFF implements Serializable {

@Column(name = "AFF_NAME")
private String AFF_NAME;

@Column(name = "AFF_CODE")
private String AFF_CODE;

@Id
@Column(name = "AFF_ID")
private String AFF_ID;

private Set&lt;AFF_CONFIG&gt; someAff = new HashSet&lt;AFF_CONFIG&gt;();

@LazyCollection(LazyCollectionOption.TRUE)
@OneToMany(cascade = CascadeType.ALL, mappedBy = "aff")

public Set&lt;AFF_CONFIG&gt; getSomeAff() {
    return someAff;
}

public void setSomeAff(Set&lt;AFF_CONFIG&gt; someAff) {
    this.someAff = someAff;
}

public String getAFF_ID() {
    return AFF_ID;
}

public void setAFF_ID(String aFF_ID) {
    AFF_ID = aFF_ID;
}

public String getAFF_NAME() {
    return AFF_NAME;
}

public void setAFF_NAME(String aFF_NAME) {
    AFF_NAME = aFF_NAME;
}

public String getAFF_CODE() {
    return AFF_CODE;
}

public void setAFF_CODE(String aFF_CODE) {
    AFF_CODE = aFF_CODE;
}
</code></pre>

<p>Since this is many to one relation I created set type in one and object type in another as defined in other places.Created a repository by extending crud and added a  query. Excise the bunch of different annotations, I included them in hoping to solve the null entry. </p>

<pre><code>@Repository
public interface MarketRepository extends       CrudRepository&lt;AFF_CONFIG,String&gt; {

Page&lt;AFF_CONFIG&gt; findAll(Pageable pageable);

 @Query("Select a,b from AFF_CONFIG a, AFF b where     a.AFF_ID = b.AFF_ID" )
public List&lt;AFF_CONFIG&gt; getAffData();
} 
</code></pre>

<p>the applicatoin is working fine even after some tinkering until I Included these annotations. Now there is this error:</p>

<blockquote>
  <p>Caused by: org.hibernate.MappingException: Could not determine type for: java.util.Set, at table: aff.</p>
</blockquote>