This following code works properly, but I wanted it to have in generic style.
I tried to write it in a generic way, but I had some problems.
I have a method that is to get some data from two collections from MongoDB.
I use MongoOperations from package org.springframework.data.mongodb.core to handle MongoDB operations. The method find which I am calling, needs parameters: query, and a class of which the Mongo Collection is made of. Classes EvaluationWork and ArchivalWork implement an interface WorkContainer.
What I'd like to do is to make use of that T generic parameter, which is upper bounded by WorkContainer, by make generic the call of find method, instead of EvaluationWork.class and ArchivalWork.class if possible. And I am also curious whether is possible to have the function convertToWorkWithId generic and the possibility to call it in the same way as now, without casting (.map(w->convertToWorkWithId((T)w))) ?
public abstract class AbstractWorkMongoDao<T extends WorkContainer> {
protected WorkWithId convertToWorkWithId(WorkContainer evaluationWork) {
return evaluationWork.getWorkWithId();
}
/* there is some code here */
public List<WorkWithId> getByDate(String institutionId, String startDate, String endDate, boolean repository) {
Query query = buildSearchQuery(institutionId, startDate, endDate);
List<WorkWithId> workWithIds = mongoOperations.find(query, EvaluationWork.class)
.stream()
.map(this::convertToWorkWithId)
.collect(Collectors.toList());
if(repository){
workWithIds.addAll(mongoOperations.find(query, ArchivalWork.class)
.stream()
.map(this::convertToWorkWithId)
.collect(Collectors.toList())
);
}
return workWithIds;
}
}
I am trying to convert something like this in jOOQ:
select foo from bar
order by field(foo, 'value1', 'something-else', 'value3')
on a select query, like:
SelectQuery<Record> query = ...
query.addSelect(BAR.FOO);
query.addFrom(BAR);
query.addOrderBy( ... ? ... )
How does one add the last bit?
Background
What I am trying to accomplish is basically described here: MySQL - ORDER BY values within IN(). In my case, I have a generic batch load function that uses 'where field in(..)' and I want to preserve order. This works as I need it to using plain SQL, but I need to add this bit to a dynamically constructed query with jOOQ.
Whenever you hit jOOQ's limits, resort to plain SQL. You can write your own field function like this:
class MyDSL {
public static Field<Integer> field(Field<String> search, String in1) {
return field(search, DSL.val(in1));
}
public static Field<Integer> field(Field<String> search, Field<String> in1) {
return DSL.field("field({0}, {1})", Integer.class, search, in1);
}
public static Field<Integer> field(Field<String> search,
String in1,
String in2) {
return field(search, val(in1), val(in2));
}
public static Field<Integer> field(Field<String> search,
Field<String> in1,
Field<String> in2) {
return DSL.field("field({0}, {1}, {2})", Integer.class, search, in1, in2);
}
// ... or, support a varargs function variant, too
}
And now use that in all your statements:
query.addOrderBy( MyDSL.field(BAR.FOO, "value1", "something-else", "value3") );
This seems to do the trick. Not sure if there is a better answer,
Field[] args = new Field[]{DSL.field("foo"),
DSL.val("value1"), DSL.val("something-else"), DSL.val("value3")}
query.addOrderBy(DSL.function("field", SQLDataType.INTEGER, args));
You can use something like to convert following sql to jooq. Here 'sortAsc' is used to sort according to the given value order.
SQL
select foo from bar order by field(foo, 'value1', 'something-else', 'value3')
JOOQ
DSL()
.select(BAR.FOO)
.from(BAR)
.orderBy(BAR.FOO.sortAsc('value11', 'something-else', 'value3'))
.fetch()
I have a SearchCriteria POJO class
public class SearchCriteria{
private int empId;
private String empName;
private String empAddress;
private String empDesignation,
:
:
//getter + setters
}
I have a returnAllEmployees method in other class
public List<Employees> returnAllEmployees (){
// makes a db call which has lot of joins and returns info for all the employees
}
now my question is I have to filter out the result of returnAllEmployees() based on the search criteria passed i.e. if empName field of searchcriteria is populated as "ABC", the filter list should contain details of all the employees as ABC.
Similarly, if search criteria contains empName="ABC" and empDesignation="engineer", it should filter out the list containing all the employees having name abc and designation as engineer
I know it is possible by using if-else but that would create a lot of lines of codes
Your best solution is to use Java 8 streams. They are perfect for this:
List<Employee> listOfEngineersCalledFred = getAllEmployees().stream()
.filter(emp -> emp.getName().equals("Fred"))
.filter(emp -> emp.getDesignation().equals("Engineer"))
.collect(Collectors.toList());
A technique that I personally find useful and neat is to add static methods that return predicates instead of using getters:
class Employee {
public static Predicate<Employee> hasName(String name) {
return emp -> emp.name.equals(name);
}
}
These can then be used, for example, to find all employees not call Fred:
streamAllEmployees()
.filter(Employee.hasName("Fred").negate())
...
Which seems neater and more deliberate than exposing the field with a getter.
You also might consider converting your getAllEmployees to streamAllEmployees:
public Stream<Employee> streamAllEmployees() {
return employeeList.stream();
}
Then you are telling the user they can do things with the employee objects in the list rather than the list itself.
The nice thing about returning it as a stream is that once you have filtered it you can easily count, group, sort, remove duplicates, get first n etc. You can even trivially convert it to use multiple threads if you are filtering large numbers of items.
For example:
Map<String, Employee> employeesByDesignation = streamAllEmployees()
.collect(Collectors.groupingBy(emp -> emp.getDesignation()));
They are very powerful and worth learning and using.
How to call this pattern, and is there any existing apache-commons utility for this:
class Person {
String getName();
}
List<Person> persons = ...;
// create a dynamic bean on the fly, which can be used as:
Object personXxxx = transformListOfBeans(Person.class, persons);
// so each of the bean properties now returns the list of the original property:
List<String> personNames = personXxxx.name;
// i.e. the transformation creates a new "type":
class PersonXxxx {
List<String> getName();
}
How to call this kind of transformation? A proxy should keep the method signatures. So it is not a proxy, neither decorator.
Well, I can simply rename the generated property names to plural form, like:
personXxxx.names
This is no problem. I want to know if such pattern was already known so I don't have to choose the appropriate words myself.
I don't think a tool exists for this.
You have to code it :
List<String> names = new ArrayList<String>(persons.size());
for (Person person : persons) {
names.add(person.getName());
}
Maybe you can use introspection to be more generic, but code is really simple.
I don't think there is a pattern as such, but guava provides a simple way of transforming a collection of one to another. For the example:
List<Person> persons = ...;
Iterable<String> names = Iterables.transform(persons, new Function<Person, String>() {
#Override
public String apply(Person person) {
return person.getName();
}
});
A possibility is to declare an interface for all the methods, e.g. (leading I for clarity) INamable, IAgeable, ISexable etc. Cast the List<Person> to List<ISomething>. Obviously this has issues.
We'd like to use only annotations with MyBatis; we're really trying to avoid xml. We're trying to use an "IN" clause:
#Select("SELECT * FROM blog WHERE id IN (#{ids})")
List<Blog> selectBlogs(int[] ids);
MyBatis doesn't seem able to pick out the array of ints and put those into the resulting query. It seems to "fail softly" and we get no results back.
It looks like we could accomplish this using XML mappings, but we'd really like to avoid that. Is there a correct annotation syntax for this?
I believe the answer is the same as is given in this question. You can use myBatis Dynamic SQL in your annotations by doing the following:
#Select({"<script>",
"SELECT *",
"FROM blog",
"WHERE id IN",
"<foreach item='item' index='index' collection='list'",
"open='(' separator=',' close=')'>",
"#{item}",
"</foreach>",
"</script>"})
List<Blog> selectBlogs(#Param("list") int[] ids);
The <script> element enables dynamic SQL parsing and execution for the annotation. It must be very first content of the query string. Nothing must be in front of it, not even white space.
Note that the variables that you can use in the various XML script tags follow the same naming conventions as regular queries, so if you want to refer to your method arguments using names other than "param1", "param2", etc... you need to prefix each argument with an #Param annotation.
I believe this is a nuance of jdbc's prepared statements and not MyBatis. There is a link here that explains this problem and offers various solutions. Unfortunately, none of these solutions are viable for your application, however, its still a good read to understand the limitations of prepared statements with regards to an "IN" clause. A solution (maybe suboptimal) can be found on the DB-specific side of things. For example, in postgresql, one could use:
"SELECT * FROM blog WHERE id=ANY(#{blogIds}::int[])"
"ANY" is the same as "IN" and "::int[]" is type casting the argument into an array of ints. The argument that is fed into the statement should look something like:
"{1,2,3,4}"
Had some research on this topic.
one of official solution from mybatis is to put your dynamic sql in #Select("<script>...</script>"). However, writing xml in java annotation is quite ungraceful. think about this #Select("<script>select name from sometable where id in <foreach collection=\"items\" item=\"item\" seperator=\",\" open=\"(\" close=\")\">${item}</script>")
#SelectProvider works fine. But it's a little complicated to read.
PreparedStatement not allow you set list of integer. pstm.setString(index, "1,2,3,4") will let your SQL like this select name from sometable where id in ('1,2,3,4'). Mysql will convert chars '1,2,3,4' to number 1.
FIND_IN_SET don't works with mysql index.
Look in to mybatis dynamic sql mechanism, it has been implemented by SqlNode.apply(DynamicContext). However, #Select without <script></script> annotation will not pass parameter via DynamicContext
see also
org.apache.ibatis.scripting.xmltags.XMLLanguageDriver
org.apache.ibatis.scripting.xmltags.DynamicSqlSource
org.apache.ibatis.scripting.xmltags.RawSqlSource
So,
Solution 1: Use #SelectProvider
Solution 2: Extend LanguageDriver which will always compile sql to DynamicSqlSource. However, you still have to write \" everywhere.
Solution 3: Extend LanguageDriver which can convert your own grammar to mybatis one.
Solution 4: Write your own LanguageDriver which compile SQL with some template renderer, just like mybatis-velocity project does. In this way, you can even integrate groovy.
My project take solution 3 and here's the code:
public class MybatisExtendedLanguageDriver extends XMLLanguageDriver
implements LanguageDriver {
private final Pattern inPattern = Pattern.compile("\\(#\\{(\\w+)\\}\\)");
public SqlSource createSqlSource(Configuration configuration, String script, Class<?> parameterType) {
Matcher matcher = inPattern.matcher(script);
if (matcher.find()) {
script = matcher.replaceAll("(<foreach collection=\"$1\" item=\"__item\" separator=\",\" >#{__item}</foreach>)");
}
script = "<script>" + script + "</script>";
return super.createSqlSource(configuration, script, parameterType);
}
}
And the usage:
#Lang(MybatisExtendedLanguageDriver.class)
#Select("SELECT " + COLUMNS + " FROM sometable where id IN (#{ids})")
List<SomeItem> loadByIds(#Param("ids") List<Integer> ids);
I've made a small trick in my code.
public class MyHandler implements TypeHandler {
public void setParameter(PreparedStatement ps, int i, Object parameter, JdbcType jdbcType) throws SQLException {
Integer[] arrParam = (Integer[]) parameter;
String inString = "";
for(Integer element : arrParam){
inString = "," + element;
}
inString = inString.substring(1);
ps.setString(i,inString);
}
And I used this MyHandler in SqlMapper :
#Select("select id from tmo where id_parent in (#{ids, typeHandler=ru.transsys.test.MyHandler})")
public List<Double> getSubObjects(#Param("ids") Integer[] ids) throws SQLException;
It works now :)
I hope this will help someone.
Evgeny
Other option can be
public class Test
{
#SuppressWarnings("unchecked")
public static String getTestQuery(Map<String, Object> params)
{
List<String> idList = (List<String>) params.get("idList");
StringBuilder sql = new StringBuilder();
sql.append("SELECT * FROM blog WHERE id in (");
for (String id : idList)
{
if (idList.indexOf(id) > 0)
sql.append(",");
sql.append("'").append(id).append("'");
}
sql.append(")");
return sql.toString();
}
public interface TestMapper
{
#SelectProvider(type = Test.class, method = "getTestQuery")
List<Blog> selectBlogs(#Param("idList") int[] ids);
}
}
In my project, we are already using Google Guava, so a quick shortcut is.
public class ListTypeHandler implements TypeHandler {
#Override
public void setParameter(PreparedStatement ps, int i, Object parameter, JdbcType jdbcType) throws SQLException {
ps.setString(i, Joiner.on(",").join((Collection) parameter));
}
}
In Oracle, I use a variant of Tom Kyte's tokenizer to handle unknown list sizes (given Oracle's 1k limit on an IN clause and the aggravation of doing multiple INs to get around it). This is for varchar2, but it can be tailored for numbers (or you could just rely on Oracle knowing that '1' = 1 /shudder).
Assuming you pass or perform myBatis incantations to get ids as a String, to use it:
select #Select("SELECT * FROM blog WHERE id IN (select * from table(string_tokenizer(#{ids}))")
The code:
create or replace function string_tokenizer(p_string in varchar2, p_separator in varchar2 := ',') return sys.dbms_debug_vc2coll is
return_value SYS.DBMS_DEBUG_VC2COLL;
pattern varchar2(250);
begin
pattern := '[^(''' || p_separator || ''')]+' ;
select
trim(regexp_substr(p_string, pattern, 1, level)) token
bulk collect into
return_value
from
dual
where
regexp_substr(p_string, pattern, 1, level) is not null
connect by
regexp_instr(p_string, pattern, 1, level) > 0;
return return_value;
end string_tokenizer;
You could use a custom type handler to do this. For example:
public class InClauseParams extends ArrayList<String> {
//...
// marker class for easier type handling, and avoid potential conflict with other list handlers
}
Register the following type handler in your MyBatis config (or specify in your annotation):
public class InClauseTypeHandler extends BaseTypeHandler<InClauseParams> {
#Override
public void setNonNullParameter(final PreparedStatement ps, final int i, final InClauseParams parameter, final JdbcType jdbcType) throws SQLException {
// MySQL driver does not support this :/
Array array = ps.getConnection().createArrayOf( "VARCHAR", parameter.toArray() );
ps.setArray( i, array );
}
// other required methods omitted for brevity, just add a NOOP implementation
}
You can then use them like this
#Select("SELECT * FROM foo WHERE id IN (#{list})"
List<Bar> select(#Param("list") InClauseParams params)
However, this will not work for MySQL, because the MySQL connector does not support setArray() for prepared statements.
A possible workaround for MySQL is to use FIND_IN_SET instead of IN:
#Select("SELECT * FROM foo WHERE FIND_IN_SET(id, #{list}) > 0")
List<Bar> select(#Param("list") InClauseParams params)
And your type handler becomes:
#Override
public void setNonNullParameter(final PreparedStatement ps, final int i, final InClauseParams parameter, final JdbcType jdbcType) throws SQLException {
// note: using Guava Joiner!
ps.setString( i, Joiner.on( ',' ).join( parameter ) );
}
Note: I don't know the performance of FIND_IN_SET, so test this if it is important
I had done this with postgresql.
#Update('''
UPDATE sample_table
SET start = null, finish = null
WHERE id=ANY(#{id});
''')
int resetData(#Param("id") String[] id)
ANY works like the IN.
Code above is using groovy but can be converted into java by replacing the single quotes into double.