改进 EFCore Query 以实现快速操作

问题描述

我读了一个sqlite数据库(数据库大小3MB左右，所以信息不多，每张表大概有1、2000行)并从中提取信息，然后我把这些信息添加到一个新的数据库.整个操作大约需要 40 秒.

I read a sqlite database (The size of the database is about 3 MB, So there is not much information, each table is about 1 or 2 thousand rows) and extract information from it, Then I add this information to a new database.The whole operation takes about 40 seconds.

我怎样才能减少这个时间并尽快完成操作?(任务、并行、异步……)

How can I reduce this time and get the operation done as quickly as possible? (Task, Parallel, async,...)

我目前正在使用此代码:

I am currently using this code:

await Task.Run(async () =>
            {
                var pkgs = new ManifestTable();
                var mydb = new dbContext();
                await mydb.Database.EnsureDeletedAsync();
                await mydb.Database.EnsureCreatedAsync();
                using (var msixDB = new MSIXContext())
                {
                    foreach (var item in await msixDB.IdsMSIXTable.ToListAsync())
                    {
                        var rowId = item.rowid;
                        var manifests = await msixDB.Set<ManifestMSIXTable>().Where((e) => e.id == rowId).ToListAsync();

                        foreach (var manifest in manifests)
                        {
                            pkgs = new ManifestTable();
                            pkgs.PackageId = item.id;


                            var productMap = await msixDB.ProductCodesMapMSIXTable.FirstOrDefaultAsync((e) => e.manifest == manifest.rowid);
                            if (productMap != null)
                            {
                                var prdCode = await msixDB.ProductCodesMSIXTable.FirstOrDefaultAsync((e) => e.rowid == productMap.productcode);
                                if (prdCode != null)
                                {
                                    pkgs.ProductCode = prdCode.productcode;
                                }
                            }
                            var publisherMap = await msixDB.Set<PublishersMapMSIXTable>().FirstOrDefaultAsync((e) => e.manifest == manifest.rowid);

                            if (publisherMap != null)
                            {
                                var publisher = await msixDB.PublishersMSIXTable.FirstOrDefaultAsync((e) => e.rowid == publisherMap.norm_publisher);

                                if (publisher != null)
                                {
                                    pkgs.Publisher = publisher.norm_publisher;
                                }
                            }

                            var pathPart = manifest.pathpart;
                            var yml = await msixDB.PathPartsMSIXTable.FirstOrDefaultAsync((e) => e.rowid == pathPart);
                            if (yml != null)
                            {
                                pkgs.YamlName = yml.pathpart;
                            }

                            var version = await msixDB.VersionsMSIXTable.FirstOrDefaultAsync((e) => e.rowid == manifest.version);
                            if (version != null)
                            {
                                pkgs.Version = version.version;
                            }
                            await mydb.ManifestTable.AddAsync(pkgs);
                        }
                    }
                     await mydb.SaveChangesAsync();
                }

            });

推荐答案

将数据库视为对象存储是有史以来最糟糕的想法.您必须尽可能减少数据库往返次数.在您的情况下 - 只需一个请求.如果您不知道哪个部分慢，也不要玩 Task.Run、Parallel 等.在您的情况下 - 数据库往返.

Treating database as object storage is worst idea ever. You have to reduce database roundtrips as it is possible. In your case - by just one request. Also do not play with Task.Run, Parallel, etc. if you do not know which part is slow. In your case - database roundtrips.

var mydb = new dbContext();
await mydb.Database.EnsureDeletedAsync();
await mydb.Database.EnsureCreatedAsync();

using (var msixDB = new MSIXContext())
{
    var query =
        from item in msixDB.IdsMSIXTable
        from manifest in msixDB.Set<ManifestMSIXTable>().Where(e => e.id == item.rowId)
        from productMap in msixDB.ProductCodesMapMSIXTable.Where(e => e.manifest == manifest.rowid).Take(1).DefaultIfEmpty()
        from prdCode in msixDB.ProductCodesMSIXTable.Where(e => e.rowid == productMap.productcode).Take(1).DefaultIfEmpty();
        from publisherMap in msixDB.Set<PublishersMapMSIXTable>().Where(e => e.manifest == manifest.rowid).Take(1).DefaultIfEmpty()
        from publisher in msixDB.PublishersMSIXTable.Where(e => e.rowid == publisherMap.norm_publisher).Take(1).DefaultIfEmpty()
        from yml in msixDB.PathPartsMSIXTable.Where(e => e.rowid == manifest.pathpart).Take(1).DefaultIfEmpty()
        from version in msixDB.VersionsMSIXTable.Where(e => e.rowid == manifest.version).Take(1).DefaultIfEmpty()
        select new ManifestTable
        {
            PackageId = item.id,
            ProductCode = prdCode.productcode,
            Publisher = publisher.norm_publisher,
            YamlName = yml.pathpart,
            Version = version.version
        };

    mydb.ManifestTable.AddRange(await query.ToListAsync());
    await mydb.SaveChangesAsync();
}

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