确切地说，“信息”是什么？精致的缓存？ [英] What exactly is the "information" that dapper caches?

问题描述

在Dapper的文档中此处指出：

On Dapper's documentation found here it states:

限制和警告

Dapper会缓存有关其运行的每个查询的信息 ，这允许它快速实现对象并快速处理参数。当前的实现将这些信息缓存在ConcurrentDictionary对象中。

Dapper caches information about every query it runs, this allow it to materialize objects quickly and process parameters quickly. The current implementation caches this information in a ConcurrentDictionary object."

确切是什么？这是否意味着？
例如：是缓存返回的数据，还是查询本身，还是两者都缓存？

What exactly does this mean? Ex: Is it caching returned data, or the query itself, or bits of both?

它还说 此[缓存的]数据永远不会被刷新。如果要查询的表的设计方案已更改，这对缓存的信息有何影响？

It also says that "this [cached] data is never flushed". How does this effect the "cached information" if the design schema of the table(s) you are querying is changed?

推荐答案

据我所知，每个查询都会根据SQL查询，其命令类型和参数发出 Identity 。缓存是具有并发访问权限的字典。

As far as I know has each query you issue an Identity, depending on the sql query, its command type and its parameters. The cache is a dictionary with concurrent access.

Dictionary<Identity, CacheInfo> _queryCache

此 CacheInfo 对象包含 IDataReader 和 IDBCommand 函数以及一些限制缓存量的控制计数器。

This CacheInfo object contains the IDataReader and IDBCommand functions and some control counters which limit the cached amount.

由于未缓存任何服务器端（数据库架构等），因此实际上没有任何影响。

Since no server-side (database schema etc.) are cached, it actually doesn't have any influence.

编辑：这就是Identity类的外观

Thats how the Identity class looks like used for caching.

private Identity(string sql, CommandType? commandType, string connectionString, Type type, Type parametersType, Type[] otherTypes, int gridIndex)
        {
            this.sql = sql;
            this.commandType = commandType;
            this.connectionString = connectionString;
            this.type = type;
            this.parametersType = parametersType;
            this.gridIndex = gridIndex;
            unchecked
            {
                hashCode = 17; // we *know* we are using this in a dictionary, so pre-compute this
                hashCode = hashCode * 23 + commandType.GetHashCode();
                hashCode = hashCode * 23 + gridIndex.GetHashCode();
                hashCode = hashCode * 23 + (sql == null ? 0 : sql.GetHashCode());
                hashCode = hashCode * 23 + (type == null ? 0 : type.GetHashCode());
                if (otherTypes != null)
                {
                    foreach (var t in otherTypes)
                    {
                        hashCode = hashCode * 23 + (t == null ? 0 : t.GetHashCode());
                    }
                }
                hashCode = hashCode * 23 + (connectionString == null ? 0 : connectionString.GetHashCode());
                hashCode = hashCode * 23 + (parametersType == null ? 0 : parametersType.GetHashCode());
            }
        }

这是CacheInfo

And here's the CacheInfo

class CacheInfo

        {
            public Func<IDataReader, object> Deserializer { get; set; }
            public Func<IDataReader, object>[] OtherDeserializers { get; set; }
            public Action<IDbCommand, object> ParamReader { get; set; }
            private int hitCount;
            public int GetHitCount() { return Interlocked.CompareExchange(ref hitCount, 0, 0); }
            public void RecordHit() { Interlocked.Increment(ref hitCount); }
        }

最后是缓存的容器。

static readonly System.Collections.Concurrent.ConcurrentDictionary<Identity, CacheInfo> _queryCache = new System.Collections.Concurrent.ConcurrentDictionary<Identity, CacheInfo>();

看看源代码，它写得很好，易于遵循/调试。只需将文件拖到您的项目中即可。

Have a look at the source code, its very well written and easy to follow / debug. Just drag the file into your project.

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