How to add description to columns in Entity Framework 4.3 code first using migrations?
I'm using Entity Framework 4.3.1 code first with explicit migrations. How do I add descriptions for columns either in the entity configuration classes or the migrations, so that it ends up as the description of a column in SQL server (e.g. 2008 R2)?
I know I can probably write an extension method for the DbMigration class that would register the sp_updateextendedproperty or sp_addextendedproperty procedure call as a sql migration operation inside the migration transaction and call that extension after table creation in the migration Up method. But is there an elegant built in way that I've yet to discover? Would be nice to have an attribute that the migrations' change detection logic can pick up on and generate appropritate method calls in the scaffolded migration.
Answer
I needed this too. So I spent a day and here it is:
The Code
public class DbDescriptionUpdater<TContext>
where TContext : System.Data.Entity.DbContext
{
public DbDescriptionUpdater(TContext context)
{
this.context = context;
}
Type contextType;
TContext context;
DbTransaction transaction;
public void UpdateDatabaseDescriptions()
{
contextType = typeof(TContext);
this.context = context;
var props = contextType.GetProperties(System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.Public);
transaction = null;
try
{
context.Database.Connection.Open();
transaction = context.Database.Connection.BeginTransaction();
foreach (var prop in props)
{
if (prop.PropertyType.InheritsOrImplements((typeof(DbSet<>))))
{
var tableType = prop.PropertyType.GetGenericArguments()[0];
SetTableDescriptions(tableType);
}
}
transaction.Commit();
}
catch
{
if (transaction != null)
transaction.Rollback();
throw;
}
finally
{
if (context.Database.Connection.State == System.Data.ConnectionState.Open)
context.Database.Connection.Close();
}
}
private void SetTableDescriptions(Type tableType)
{
string fullTableName = context.GetTableName(tableType);
Regex regex = new Regex(@"(\[\w+\]\.)?\[(?<table>.*)\]");
Match match = regex.Match(fullTableName);
string tableName;
if (match.Success)
tableName = match.Groups["table"].Value;
else
tableName = fullTableName;
var tableAttrs = tableType.GetCustomAttributes(typeof(TableAttribute), false);
if (tableAttrs.Length > 0)
tableName = ((TableAttribute)tableAttrs[0]).Name;
foreach (var prop in tableType.GetProperties(System.Reflection.BindingFlags.Public | System.Reflection.BindingFlags.Instance))
{
if (prop.PropertyType.IsClass && prop.PropertyType != typeof(string))
continue;
var attrs = prop.GetCustomAttributes(typeof(DisplayAttribute), false);
if (attrs.Length > 0)
SetColumnDescription(tableName, prop.Name, ((DisplayAttribute)attrs[0]).Name);
}
}
private void SetColumnDescription(string tableName, string columnName, string description)
{
string strGetDesc = "select [value] from fn_listextendedproperty('MS_Description','schema','dbo','table',N'" + tableName + "','column',null) where objname = N'" + columnName + "';";
var prevDesc = RunSqlScalar(strGetDesc);
if (prevDesc == null)
{
RunSql(@"EXEC sp_addextendedproperty
@name = N'MS_Description', @value = @desc,
@level0type = N'Schema', @level0name = 'dbo',
@level1type = N'Table', @level1name = @table,
@level2type = N'Column', @level2name = @column;",
new SqlParameter("@table", tableName),
new SqlParameter("@column", columnName),
new SqlParameter("@desc", description));
}
else
{
RunSql(@"EXEC sp_updateextendedproperty
@name = N'MS_Description', @value = @desc,
@level0type = N'Schema', @level0name = 'dbo',
@level1type = N'Table', @level1name = @table,
@level2type = N'Column', @level2name = @column;",
new SqlParameter("@table", tableName),
new SqlParameter("@column", columnName),
new SqlParameter("@desc", description));
}
}
DbCommand CreateCommand(string cmdText, params SqlParameter[] parameters)
{
var cmd = context.Database.Connection.CreateCommand();
cmd.CommandText = cmdText;
cmd.Transaction = transaction;
foreach (var p in parameters)
cmd.Parameters.Add(p);
return cmd;
}
void RunSql(string cmdText, params SqlParameter[] parameters)
{
var cmd = CreateCommand(cmdText, parameters);
cmd.ExecuteNonQuery();
}
object RunSqlScalar(string cmdText, params SqlParameter[] parameters)
{
var cmd = CreateCommand(cmdText, parameters);
return cmd.ExecuteScalar();
}
}
public static class ReflectionUtil
{
public static bool InheritsOrImplements(this Type child, Type parent)
{
parent = ResolveGenericTypeDefinition(parent);
var currentChild = child.IsGenericType
? child.GetGenericTypeDefinition()
: child;
while (currentChild != typeof(object))
{
if (parent == currentChild || HasAnyInterfaces(parent, currentChild))
return true;
currentChild = currentChild.BaseType != null
&& currentChild.BaseType.IsGenericType
? currentChild.BaseType.GetGenericTypeDefinition()
: currentChild.BaseType;
if (currentChild == null)
return false;
}
return false;
}
private static bool HasAnyInterfaces(Type parent, Type child)
{
return child.GetInterfaces()
.Any(childInterface =>
{
var currentInterface = childInterface.IsGenericType
? childInterface.GetGenericTypeDefinition()
: childInterface;
return currentInterface == parent;
});
}
private static Type ResolveGenericTypeDefinition(Type parent)
{
var shouldUseGenericType = true;
if (parent.IsGenericType && parent.GetGenericTypeDefinition() != parent)
shouldUseGenericType = false;
if (parent.IsGenericType && shouldUseGenericType)
parent = parent.GetGenericTypeDefinition();
return parent;
}
}
public static class ContextExtensions
{
public static string GetTableName(this DbContext context, Type tableType)
{
MethodInfo method = typeof(ContextExtensions).GetMethod("GetTableName", new Type[] { typeof(DbContext) })
.MakeGenericMethod(new Type[] { tableType });
return (string)method.Invoke(context, new object[] { context });
}
public static string GetTableName<T>(this DbContext context) where T : class
{
ObjectContext objectContext = ((IObjectContextAdapter)context).ObjectContext;
return objectContext.GetTableName<T>();
}
public static string GetTableName<T>(this ObjectContext context) where T : class
{
string sql = context.CreateObjectSet<T>().ToTraceString();
Regex regex = new Regex("FROM (?<table>.*) AS");
Match match = regex.Match(sql);
string table = match.Groups["table"].Value;
return table;
}
}
How To Use
In your Migrations/Configuration.cs file, add this at the end of the Seed method:
DbDescriptionUpdater<ContextClass> updater = new DbDescriptionUpdater<ContextClass>(context);
updater.UpdateDatabaseDescriptions();
Then in Package Manager Console type update-database and hit Enter.
That's it.
The code uses [Display(Name="Description here")] attribute on your entity class properties to set the description.
Please report any bug or suggest improvements.
Thanks to
I've used these code from other people and I want to say thanks:
Check if a class is derived from a generic class