如何将类项目装饰为索引,并使用ensureIndex进行相同的操作？

Question

我想在类声明中定义哪些项是索引,类似于:

public class MyClass {
    public int SomeNum { get; set; }
    [THISISANINDEX]
    public string SomeProperty { get; set; }
}

所以与ensureIndex("SomeProperty")具有相同的效果

这可能吗？

Answer 1

我认为这是一个好主意,但你必须自己做,没有内置的支持.如果您有访问层,则可以在那里执行.你需要一个属性类,就像这样;

public enum IndexConstraints
{
    Normal     = 0x00000001, // Ascending, non-indexed
    Descending = 0x00000010,
    Unique     = 0x00000100,
    Sparse     = 0x00001000, // allows nulls in the indexed fields
}

// Applied to a member
[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
public class EnsureIndexAttribute : EnsureIndexes
{
    public EnsureIndex(IndexConstraints ic = IndexConstraints.Normal) : base(ic) { }
}

// Applied to a class
[AttributeUsage(AttributeTargets.Class)]
public class EnsureIndexesAttribute : Attribute
{
    public bool Descending { get; private set; }
    public bool Unique { get; private set; }
    public bool Sparse { get; private set; }
    public string[] Keys { get; private set; }

    public EnsureIndexes(params string[] keys) : this(IndexConstraints.Normal, keys) {}
    public EnsureIndexes(IndexConstraints ic, params string[] keys)
    {
        this.Descending = ((ic & IndexConstraints.Descending) != 0);
        this.Unique = ((ic & IndexConstraints.Unique) != 0); ;
        this.Sparse = ((ic & IndexConstraints.Sparse) != 0); ;
        this.Keys = keys;
    }

}//class EnsureIndexes

然后,您可以在类或成员级别应用属性,如下所示.我发现与在类级别添加相比,在成员级别添加不太可能与架构不同步.您需要确保获得实际的元素名称而不是C#成员名称;

[CollectionName("People")]
//[EnsureIndexes("k")]// doing it here would allow for multi-key configs
public class Person 
{
    [BsonElement("k")] // name mapping in the DB schema
    [BsonIgnoreIfNull]
    [EnsureIndex(IndexConstraints.Unique|IndexConstraints.Sparse)] // name is implicit here
    public string userId{ get; protected set; }

// other properties go here
}

然后在你的数据库访问实现(或存储库)中,你需要这样的东西;

    private void AssureIndexesNotInlinable()
    {
                // We can only index a collection if there's at least one element, otherwise it does nothing
                if (this.collection.Count() > 0)
                {

                    // Check for EnsureIndex Attribute
                    var theClass = typeof(T);

                    // Walk the members of the class to see if there are any directly attached index directives
                    foreach (var m in theClass.GetProperties(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.FlattenHierarchy))
                    {
                        List<string> elementNameOverride = new List<string>(1);
                        EnsureIndexes indexAttr = null;

                        // For each members attribs
                        foreach (Attribute attr in m.GetCustomAttributes())
                        {
                            if (attr.GetType() == typeof(EnsureIndex))
                                indexAttr = (EnsureIndex)attr;

                            if (attr.GetType() == typeof(RepoElementAttribute))
                                elementNameOverride.Add(((RepoElementAttribute)attr).ElementName);

                            if ((indexAttr != null) && (elementNameOverride.Count != 0))
                                break;
                        }

                        // Index
                        if (indexAttr != null)
                        {
                            if (elementNameOverride.Count() > 0)
                                EnsureIndexesAsDeclared(indexAttr, elementNameOverride);
                            else
                                EnsureIndexesAsDeclared(indexAttr);
                        }
                    }

                    // Walk the atributes on the class itself. WARNING: We don't validate the member names here, we just create the indexes
                    // so if you create a unique index and don't have a field to match you'll get an exception as you try to add the second
                    // item with a null value on that key
                    foreach (Attribute attr in theClass.GetCustomAttributes(true))
                    {
                        if (attr.GetType() == typeof(EnsureIndexes))
                            EnsureIndexesAsDeclared((EnsureIndexes)attr);

                    }//foreach

                }//if this.collection.count

    }//AssureIndexesNotInlinable()

EnsureIndexes然后看起来像这样;

    private void EnsureIndexesAsDeclared(EnsureIndexes attr, List<string> indexFields = null)
    {
        var eia = attr as EnsureIndexes;

        if (indexFields == null)
            indexFields = eia.Keys.ToList();

        // use driver specific methods to actually create this index on the collection
        var db = GetRepositoryManager(); // if you have a repository or some other method of your own 
        db.EnsureIndexes(indexFields, attr.Descending, attr.Unique, attr.Sparse);

    }//EnsureIndexes()

请注意,您将在每次更新后放置此项,因为如果您忘记某处,则可能无法创建索引.因此,重要的是要确保优化调用,以便在通过所有反射代码之前没有要做的索引时快速返回.理想情况下,每次应用程序启动时,您只需执行一次,或者至少执行一次.因此,一种方法是使用静态标志来跟踪你是否已经这样做了,并且你需要额外的锁定保护,但过于简单,它看起来像这样;

    void AssureIndexes()
    {
        if (_requiresIndexing)
            AssureIndexesInit();
    }

这就是您在每次更新数据库时都需要的方法,如果幸运的话,JIT优化器也会更新.