通过 EF Code First 使用列表或集合来播种数据

Question

我正在为我的开发数据库添加一些种子数据。我所拥有的似乎相当笨重，有没有办法使用某种 IEnumerable 类型（例如 List 或集合）来使这更容易？

public class MusicDBInit : DropCreateDatabaseIfModelChanges<MusicContext>
{
    protected override void Seed(MusicContext db)
    {
        Band bvs = new Band { Name = "Bear vs Shark", Members = 4 };
        Band circa = new Band { Name = "Circa Survive", Members = 4 };
        Band dam = new Band { Name = "Damiera", Members = 3 };

        db.Bands.Add(bvs);
        db.Bands.Add(circa);
        db.Bands.Add(dam);

        base.Seed(db);
    }
}

Answer 1

尝试这样的事情（就像在Online Music Store MVC Sample中所做的那样：

 var bands = new List<Band>{
                     new Band { Name = "Bear vs Shark", Members = 4 },
                     new Band { Name = "Circa Survive", Members = 4 },
                     new Band { Name = "Damiera", Members = 3 }
 };


bands.ForEach(x=> db.Bands.Add(x));

Answer 2

我通常采用的另一种方法是从 XML 文件加载种子数据。一个单独的类将包含以下内容：

    private XmlNodeList readNodes(String xmlFilePath, String nodeName)
    {
        FileStream reader = new FileStream(xmlFilePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
        System.Xml.XmlDocument source = new System.Xml.XmlDocument();
        source.Load(reader);
        return source.GetElementsByTagName(nodeName);
    }

    public List<Band> readBands(String xmlFilePath)
    {
        List<Band> results = new List<Band>();
        foreach (XmlNode node in readNodes(xmlFilePath, "Band"))
        {
            results.Add(new Band { Members = node.Attributes["members"].Value, Name = node.Attributes["name"].Value });
        }
        results.Sort();
        return results;
    }

然后将以下内容添加到您的 Seed 方法中：

    foreach (Band b in seeder.readBands(AppDomain.CurrentDomain.BaseDirectory + "App_Data\\Bands.xml"))
    {
        db.bands.Add(b);
    }

您的 XML 将如下所示，并位于您的 App_Data 目录下。

<?xml version="1.0" encoding="UTF-8"?>
<bands>
    <band name="Bear vs Shark" members="4" />
    <band name="Circa Survive" members="4" />
    <band name="Damiera" members="3" />
</bands>

然后，您可以为每个要播种的表创建种子方法和 XML 文件。请记住，由于您使用的是Add 而不是AddOrUpdate，因此您很可能会在Seed 运行时添加重复项。