QueryDSL dynamic predicates

Question

I need help with QueryDSL querying. I'm using this library with Spring Data JPA. My service class:

@Service("tblActivityService")
public class TblActivityService implements AbstractService<TblActivity> {

@Resource
private TblActivityRepository tblActivityRepository;

@Override
public List<TblActivity> findAll(Predicate predicate) {
    return (List<TblActivity>) tblActivityRepository.findAll(predicate);
}
}

I have dynamic list of filters:

@Entity
@Table(name = "sys_filters")
public class SysFilter implements Serializable {
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "filter_id")
private Integer filterId;

@JoinColumn(name = "user_id", referencedColumnName = "user_id")
@ManyToOne(fetch = FetchType.EAGER)
private SysUser userId;

@Size(max = 45)
@Column(name = "table_name")
private String tableName;

@Size(max = 45)
@Column(name = "column_name")
private String columnName;

@Size(max = 45)
@Column(name = "condition")
private String condition;

@Size(max = 100)
@Column(name = "value")
private String value;


// getters & setters

}

I have column name (e.g. title) I have condition (e.g. ==, !=, >= etc.) - I can store it as symbols or words (equals etc.) And finally I have value.

The question is "how to dynamically generate predicate for my service?" Table has about 25 fields.

Predicate looks like that:

public BooleanExpression buildFilteredResult(List<SysFilter> filters) {
    //TODO do it!
    return QTblActivity.tblActivity.title.eq("Value"); 
// I need to do it dynamically for each filter in the list
}

The problem is how to invoke columnName by its string value. Do you have any suggestions?

Answer 1

It might be easier to use a mapping filter conditions to operators

Map<String, Operator> operators = ImmutableMap.of(
  "==", Ops.EQ, "!=", Ops.NE, ">", Ops.GT, "<", Ops.LT,
  ">=", Ops.GOE, "<=", Ops.LOE);

Expressions.predicate(operators.get(condition), 
  stringPath, Expressions.constant(filterValue));

Also make sure you combine your predicates properly

predicates.and(...)

returns a new predicate and leaves predicates untouched.

Maybe BooleanBuilder is what you are after?

Answer 2

A newer solution was released with spring data Gosling/Fowler. If you are creating a web app, you can use the querydsl web support that does the work for you -it reads the get parameters into a predicate and then you can use this predicate from your controller - no need to manually do that - You can customize your repository based on the search criteria (equal, like ...) needed for a particular datatype or particular entity's field. see the documentation here