QueryDSL dynamic predicates - spring

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

Answer 3

I found the solution:
public BooleanExpression buildFilteredResult(List<SysFilter> filters) {
//TODO do it!
QTblActivity qTblActivity = QTblActivity.tblActivity;
BooleanExpression expression = qTblActivity.recordState;
for (SysFilter filter : filters) {
StringPath stringPath = new StringPath(qTblActivity, filter.getColumnName());
switch (filter.getCondition()) {
case "==":
expression.and(stringPath.eq(filter.getValue()));
break;
case "!=":
expression.and(stringPath.ne(filter.getValue()));
break;
case ">":
expression.and(stringPath.gt(filter.getValue()));
break;
case "<":
expression.and(stringPath.lt(filter.getValue()));
break;
case ">=":
expression.and(stringPath.goe(filter.getValue()));
break;
case "<=":
expression.and(stringPath.loe(filter.getValue()));
break;
default:
break;
}
}
return expression;
}