Comparing two featureclasses using C#

Question

I'm sorry, I know this is a pretty simple question but am having trouble getting this to work. Basically, I have 2 linear featureclasses and they both have the same fields and spatial reference. FC1 has 675 records and FC2 only has 505 records. So how can I check what Prop_ID(s) are missing from FC2? I have some code that will copy the missing record from FC1 to FC2 but must first determine the missing Prop_ID.

many thanks

Answer 1

Since you tagged this question with arcobjects and c#, and since not all geodatabases support the SQL IN with a subquery, the following untested code shows how you could do this with System.Collections.Hashtable.

private List<int> Diff(ITable table1, ITable table2, string idfldName)
{
    // return the oid of each row in table1 whose id doesn't appear in table2
    var outList = new List<int>();

    var ht1 = HashRows(table1, idfldName);
    var ht2 = HashRows(table2, idfldName);
    foreach (object key in ht1.Keys)
    {
        if (!ht2.ContainsKey(key))
            outList.Add((int)ht1[key]);
    }
    return outList;
}

private Hashtable HashRows(ITable table, string idField)
{
    Hashtable ht = new Hashtable();
    ICursor cur = table.Search(null, true);
    try
    {
        int idx = table.FindField(idField);
        if (idx == -1)
            throw new Exception("Field not found: " + idField);
        IRow row;
        while ((row = cur.NextRow()) != null)
        {
            if(!ht.ContainsKey(row.get_Value(idx)))
                ht.Add(row.get_Value(idx),row.OID);
            else
                throw new Exception("duplicate key encountered at OID = " + row.OID);
        }
    }
    catch
    {
        throw;
    }
    finally
    {
        System.Runtime.InteropServices.Marshal.FinalReleaseComObject(cur);
    }
    return ht;
}

Answer 2

This is DBMS specific, so it may not work if you are on a filegeodb, but you could use something like PROP_ID NOT IN (select PROP_ID from FC1) in a query filter if your featureclasses aren't versioned.

This is really rough since I'm not at my workstation. This assumes you already have your IFeatureClass reference:

IQueryFilter queryFilter = new QueryFilterClass();
queryFilter.WhereClause = "PROP_ID NOT IN (select PROP_ID from FC1";

IFeatureCursor cursor = featureClass.Search(queryFilter,true);

IFeature feature = null;

  while ((feature = cur.NextFeature()) != null)
    {
        feature.get_Value(idx); // use the FindField to get idx like in Kirk's code sample
    }

---

Not sure which .NET framework you are in, but if here is an extension method:

    /// <summary>
    /// Gets the field values for a featureclass
    /// </summary>
    /// <param name="featureclass">The feature class.</param>
    /// <param name="fieldName">Name of the field.</param>
    /// <param name="whereClause">where clause for queryfilter</param>
    /// <returns>dictionary of int, object where int is the OBJECTID and object is the field value</returns>
    public static Dictionary<int, object> GetFieldValues(this IFeatureClass featureclass, string fieldName, string whereClause)
    {
        Dictionary<int, object> dictionary = new Dictionary<int, object>();

        IQueryFilter filter = new QueryFilterClass();
        filter.SubFields = string.Format("{0},{1}", featureclass.OIDFieldName, fieldName);
        filter.WhereClause = whereClause;

        int fieldIndex = featureclass.Fields.FindField(fieldName);
        if (fieldIndex > -1)
        {
            IFeatureCursor cursor = null;

            try
            {
                cursor = featureclass.Search(filter, true);
                IFeature feature = null;

                while ((feature = cursor.NextFeature()) != null)
                {                        
                    dictionary.Add(
                        feature.OID,
                        feature.get_Value(fieldIndex).Equals(System.DBNull.Value) ? null : feature.get_Value(fieldIndex));
                }
            }
            catch
            {
                throw;
            }
            finally
            {
                System.Runtime.InteropServices.Marshal.ReleaseComObject(cursor);
            }
        }

        return dictionary;
    }

And you can use it like this:

        Dictionary<int, object> featClassFieldvalues = fc1.GetFieldValues("PROP_ID", string.Empty);

        Dictionary<int, object> featClassFieldvalues2 = fc2.GetFieldValues("PROP_ID",string.Empty);

        var v = featClassFieldvalues.Values.Except(featClassFieldvalues2.Values);