Entity Framework 4.0 Automatically Truncate/Trim String Before Insert

Question

Suppose I have a table with the column Description, varchar(100). If try to insert a string with more than 100 characters, the insert will fail.

Is there a way in En

Answer 1

Here's my One-Line Solution

(invoking it is one line, the implementation is a little more)

I took the code from @elbweb and adapted it for my purposes. In my case I was parsing EDI files, some of which had 15 different levels to the hierarchy and I didn't want to explicitly specify all 15 different types - I wanted a one-liner that worked for all entity types.

It's a bit different but it's now painless to call. There is definitely a performance hit on this but it's acceptable for me. Essentially put this inside of your DbContext class and then it's a one-liner to manually call (or you can automatically call it by overriding SaveChanges to invoke it).

Code in your DbContext:

public class MyContext : DbContext
{

    ...

    public void TruncateAllStringsOnAllEntitiesToDbSize()
    {
        var objectContext = ((IObjectContextAdapter) this).ObjectContext;

        var stringMaxLengthsFromEdmx =
                objectContext.MetadataWorkspace
                             .GetItems(DataSpace.CSpace)
                             .Where(m => m.BuiltInTypeKind == BuiltInTypeKind.EntityType)
                             .SelectMany(meta => ((EntityType) meta).Properties
                             .Where(p => p.TypeUsage.EdmType.Name == "String"))
                             .Select(d => new
                                          {
                                              MaxLength = d.TypeUsage.Facets["MaxLength"].Value,
                                              PropName = d.Name,
                                              EntityName = d.DeclaringType.Name
                                          })
                             .Where(d => d.MaxLength is int)
                             .Select(d => new {d.PropName, d.EntityName, MaxLength = Convert.ToInt32(d.MaxLength)})
                             .ToList();

        var pendingEntities = ChangeTracker.Entries().Where(e => e.State == EntityState.Added || e.State == EntityState.Modified).Select(x => x.Entity).ToList();
        foreach (var entityObject in pendingEntities)
        {
            var relevantFields = stringMaxLengthsFromEdmx.Where(d => d.EntityName == entityObject.GetType().Name).ToList();

            foreach (var maxLengthString in relevantFields)
            {
                var prop = entityObject.GetType().GetProperty(maxLengthString.PropName);
                if (prop == null) continue;

                var currentValue = prop.GetValue(entityObject);
                var propAsString = currentValue as string;
                if (propAsString != null && propAsString.Length > maxLengthString.MaxLength)
                {
                    prop.SetValue(entityObject, propAsString.Substring(0, maxLengthString.MaxLength));
                }
            }
        }
    }
}

Consumption

try
{
    innerContext.TruncateAllStringsOnAllEntitiesToDbSize();
    innerContext.SaveChanges();
}
catch (DbEntityValidationException e)
{
    foreach (var err in e.EntityValidationErrors)
    {
        log.Write($"Entity Validation Errors: {string.Join("\r\n", err.ValidationErrors.Select(v => v.PropertyName + "-" + v.ErrorMessage).ToArray())}");
    }
    throw;
}

Before this code, the SaveChanges would trigger the catch in my example above when you tried inserting a string that was too large. After adding the TruncateAllStringsOnAllEntitiesToDbSize line, it works great now! I'm sure there are some optimizations that can go into this, so do please critique/contribute! :-)

Note: I have only tried this on EF 6.1.3