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View Counter

Execute INCR on each view to increment a Redis counter.

Data Structure​

Key demo:views:article:a1001 stores an integer such as 2 in a String.

Mapping​

Use Long directly without an entity. GET returns null for a missing key; INCR starts from zero when the key is missing.

Mapper​

ViewCounterMapper.java
package com.example.redis;

import net.hasor.dbvisitor.mapper.Param;
import net.hasor.dbvisitor.mapper.Query;
import net.hasor.dbvisitor.mapper.SimpleMapper;

@SimpleMapper
public interface ViewCounterMapper {
    @Query("INCR #{key}")
    long increment(@Param("key") String key);

    @Query("GET #{key}")
    Long count(@Param("key") String key);
}

Calling the Mapper​

Run inside the Session created above:

ViewCounterMapper mapper = session.createMapper(ViewCounterMapper.class);
String key = "demo:views:article:a1001";

Long before = mapper.count(key);
long first = mapper.increment(key);
long second = mapper.increment(key);
Long total = mapper.count(key);

Starting with a missing key, before = null, first = 1, second = 2 and total = 2.

Notes​

  • INCR returns the new value, so the Mapper uses @Query rather than interpreting it as an update count.
  • Do not emulate increment with GET followed by SET: concurrent views can lose increments. Store only signed 64-bit integers in the key.