Question

I have an project using Hibernate. This has a class named Question. Each Question has a difficulty level (1,2,3); Each Question also has an attribute is field (a,b,c,d,e,f,g,h,i,k);

附录一有100个问题。我想随机地问20个问题,条件是:

7 questions in level 1
7 questions in level 2
6 questions in level 3.
Each field have at least 1 question

谢意

Answer 1

First of all, I think this problem is too difficult to be solved by using a Hibernate query, or even a set of Hibernate queries.

在此,我将如何做:

load all 100 questions in memory
create a Map<Field, List<Question>>, and shuffle all the lists in this map
for each field, take the first question of the corresponding list that has an acceptable level
Once you have one question in every field, take all the remaining questions, put them in a list, shuffle the list, and iterate over the list. Each time a question has a level which is acceptable, take it. Do that until you have your 20 questions.

如果每个领域都得到保证,至少每一级都有问题,那么这项工作就应当进行。如果情况并非如此,那就更加困难。

If you have much more questions that 100, and they can t be loaded in memory, you could use the same kind of algorithm, but use random queries to select the questions:

issue one query per field to find a question in each field. The where clause should only accept the given field, and should only accept the levels which are still acceptable.
issue a query to find N questions randomly (with N being equal to 50, for example, and with a where clause which only accepts the remaining levels), and take the first 10 acceptable questions. If there are less than 10 acceptable questions, try again. There should be at most 3 such queries. Make sure your where clause rejects the IDs of the questions which have already been loaded.

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