How to get fully materialized query from querydsl

问题

I am trying to use querydsl for building dynamic queries for dynamic schemas. I am trying to get just the query instead of having to actually execute it.

So far I have faced two issues: - The schema.table notation is absent. Instead I only get the table name. - I have been able to get the query but it separates out the variables and puts '?' instead which is understandable. But I am wondering if there is some way to get fully materialized query including the parameters.

Here is my current attempt and result(I am using MySQLTemplates to create the configuration):

private SQLTemplates templates = new MySQLTemplates();
private Configuration configuration = new Configuration(templates); 

String table = "sometable"
Path<Object> userPath = new PathImpl<Object>(Object.class, table);
StringPath usernamePath = Expressions.stringPath(userPath, "username");
NumberPath<Long> idPath = Expressions.numberPath(Long.class, userPath, "id");
SQLQuery sqlQuery = new SQLQuery(connection, configuration)
  .from(userPath).where(idPath.eq(1l)).limit(10);
String query = sqlQuery.getSQL(usernamePath).getSQL();
return query;

And what I get is:

select sometable.username
from sometable
where sometable.id = ?
limit ?

What I wanted to get was:

select sometable.username
from someschema.sometable
where sometable.id = ?
limit ?

Update: I came up with this sort of hack to get parameters materialized(Not ideal and would love better solution) But still could not get Schema.Table notation to work:

Hack follows. Please suggest cleaner QueryDsl way of doing it:

String query = cleanQuery(sqlQuery.getSQL(usernamePath));

private String cleanQuery(SQLBindings bindings){
    String query = bindings.getSQL();
    for (Object binding : bindings.getBindings()) {
        query = query.replaceFirst("\\?", binding.toString());
    }
    return query;
}

回答1:

To enable schema printing use the following pattern

SQLTemplates templates = MySQLTemplates.builder()
    .printSchema()
    .build();

SQLTemplates subclasses were used before, but since some time the builder pattern is the official way to customize the templates http://www.querydsl.com/static/querydsl/3.3.1/reference/html/ch02s03.html#d0e904

And to enable direct serialization of literals use

//configuration level
configuration.setUseLiterals(true);

//query level
configuration.setUseLiterals(true);

Here is a full example

// configuration
SQLTemplates templates = MySQLTemplates.builder()
    .printSchema()
    .build();
Configuration configuration = new Configuration(templates);

// querying
SQLQuery sqlQuery = new SQLQuery(connection, configuration)
    .from(userPath).where(idPath.eq(1l)).limit(10);
sqlQuery.setUseLiterals(true);    
String query = sqlQuery.getSQL(usernamePath).getSQL();

If you always just want the SQL query string out, move setUseLiterals from query to configuration.

Concerning the usage of Querydsl expressions the usage of code generation like documented here is advised http://www.querydsl.com/static/querydsl/3.3.1/reference/html/ch02s03.html

It will make your code typesafe, compact and readable.

If you want to try Querydsl without code generation you can replace

Path<Object> userPath = new PathImpl<Object>(Object.class, variable);

with

Path<Object> userPath = new RelationalPathBase<Object>(Object.class, variable, schema, table);

回答2:

When working with QueryDSL, you must provide a template for the database platform to build the query for. I see you are already are doing this here:

private SQLTemplates templates = new MySQLTemplates();
private Configuration configuration = new Configuration(templates);

To make the schema name appear in the generated query, the only way I have found to do this is (there may be an easier way) is to extend the template class and explicitly call this.setPrintSchema(true); inside the constructor. Here is a class that should work for MySql:

import com.mysema.query.sql.MySQLTemplates;

public class NewMySqlTemplates extends MySQLTemplates {

    public NewMySqlTemplates() {
        super('\\', false);
    }

    public NewMySqlTemplates(boolean quote) {
        super('\\', quote);
    }

    public NewMySqlTemplates(char escape, boolean quote) {
        super(escape, quote);
        this.setPrintSchema(true);
    }

}

Then simply use this NewMySqlTemplates class in place of the MySQLTemplates class like this:

private SQLTemplates templates = new NewMySQLTemplates();
private Configuration configuration = new Configuration(templates);

I have this working using PostgresTemplates, so I may have a typo or mistake in the NewMySqlTemplates class above, but you should be able to get it to work. Good luck!

来源：https://stackoverflow.com/questions/21689222/how-to-get-fully-materialized-query-from-querydsl

标签

java

sql

database

querydsl

database-agnostic