java - 为 SQL 查询设计 Java 对象

Question

有没有什么好的工具/框架可以为 SQL 查询生成 Java 对象？

Answer 1

QueryDsl从您的 Hibernate、JPA 或 JDO 类自动创建查询对象，而且还 from your DB schema .

Querying with Querydsl SQL is as simple as this :

QCustomer customer = new QCustomer("c");

SQLTemplates dialect = new HSQLDBTemplates(); // SQL-dialect
SQLQuery query = new SQLQueryImpl(connection, dialect); 
List<String> lastNames = query.from(customer)
    .where(customer.firstName.eq("Bob"))
    .list(customer.lastName);

它也是supports subqueries :

To create a subquery you create a SQLSubQuery instance, define the query parameters via from, where etc and use unique or list to create a subquery, which is just a type-safe Querydsl expression for the query. unique is used for a unique (single) result and list for a list result.

query.from(customer).where(
  customer.status.eq(
      new SQLSubQuery().from(customer2).unique(customer2.status.max()))
  .list(customer.all())  

Another example

query.from(customer).where(  
  customer.status.in(new SQLSubQuery().from(status).where(
    status.level.lt(3)).list(status.id))  
  .list(customer.all())