使用Linq按属性名称和值匹配对象

Question

I need to be able to match an object to a record by matching property names and values using a single Linq query. I don't see why this shouldn't be possible, but I haven't been able to figure out how to make this work. Right now I can do it using a loop but this is slow.

Heres the scenario:

I have tables set up that store records of any given entity by putting their primary keys into an associated table with the key's property name and value.

If I have a random object at run-time, I need to be able to check if a copy of that object exists in the database by checking if the object has property names that match all of the keys of a record in the database ( this would mean that they would be the same type of object) and then checking if the values for each of the keys match, giving me the same record.

Here's how I got it to work using a loop (simplified a bit):

public IQueryable<ResultDataType> MatchingRecordFor(object entity)
{
    var result = Enumerable.Empty<ResultDataType>();
    var records = _context.DataBaseRecords

    var entityType = entity.GetType();
    var properties = entityType.GetProperties().Where(p => p.PropertyType.Namespace == "System");

    foreach (var property in properties)
    {
        var name = property.Name;
        var value = property.GetValue(entity);
        if (value != null)
        {
            var matchingRecords = records.Where(c => c.DataBaseRecordKeys.Any(k => k.DataBaseRecordKeyName == name && k.DataBaseRecordValue == value.ToString()));
            if (matchingRecords.Count() > 0)
            {
                records = matchingRecords;
            }
        }
    }

    result = (from c in records
                from p in c.DataBaseRecordProperties
                select new ResultDataType()
                {
                    ResultDataTypeId = c.ResultDataTypeID,
                    SubmitDate = c.SubmitDate,
                    SubmitUserId = c.SubmitUserId,
                    PropertyName = p.PropertyName
                });

    return result.AsQueryable();
}

The last statement joins a property table related to the database record with information on all of the properties.

This works well enough for a single record, but I'd like to get rid of that loop so that I can speed things up enough to work on many records.

Answer 1

using System.Reflection;

public IQueryable<ResultDataType> MatchingRecordFor(object entity)
{
    var records = _context.DataBaseRecords;

    var entityType = entity.GetType();
    var properties = entityType.GetProperties().Where(p => p.PropertyType.Namespace == "System");

    Func<KeyType, PropertyInfo, bool> keyMatchesProperty =
       (k, p) => p.Name == k.DataBaseRecordKeyName && p.GetValue(entity).ToString() == k.DataBaseRecordValue;

    var result =
        from r in records
        where r.DataBaseRecordKeys.All(k => properties.Any(pr => keyMatchesProperty(k, pr)))
        from p in r.DataBaseRecordProperties
        select new ResultDataType()
        {
            ResultDataTypeId = r.ResultDataTypeId,
            SubmitDate = r.SubmitDate,
            SubmitUserId = r.SubmitUserId,
            PropertyName = p.PropertyName
        });

    return result.AsQueryable();
}

Hopefully I got that query language right. You'll have to benchmark it to see if it's more efficient than your original approach.

edit: This is wrong, see comments