/// <summary>
/// Returns an object of a specified type whose value is equivalent to a specified object.
/// </summary>
/// <param name="value">An object to convert.</param>
/// <param name="conversionType">The type of object to return.</param>
/// <param name="mappingSchema">A mapping schema that defines custom converters.</param>
/// <returns>An object whose type is <i>conversionType</i> and whose value is equivalent to <i>value</i>.</returns>
public static object ChangeType([CanBeNull] object value, [NotNull] Type conversionType, MappingSchema mappingSchema = null)
{
Code.NotNull(conversionType, nameof(conversionType));
if (value == null || value is DBNull)
{
return(mappingSchema == null?
DefaultValue.GetValue(conversionType) :
mappingSchema.GetDefaultValue(conversionType));
}
if (value.GetType() == conversionType)
{
return(value);
}
var from = value.GetType();
var to = conversionType;
var key = new { from, to };
var converters = mappingSchema == null ? _converters : mappingSchema.Converters;
if (!converters.TryGetValue(key, out var l))
{
var li =
ConvertInfo.Default.Get(value.GetType(), to) ??
ConvertInfo.Default.Create(mappingSchema, value.GetType(), to);
var b = li.CheckNullLambda.Body;
var ps = li.CheckNullLambda.Parameters;
var p = Expression.Parameter(typeof(object), "p");
var ex = Expression.Lambda <Func <object, object> >(
Expression.Convert(
b.Transform(e =>
e == ps[0] ?
Expression.Convert(p, e.Type) :
IsDefaultValuePlaceHolder(e) ?
new DefaultValueExpression(mappingSchema, e.Type) :
e),
typeof(object)),
p);
l = ex.Compile();
converters[key] = l;
}
return(l(value));
}
public object GetDefaultValue([NotNull] Type type)
{
Code.NotNull(type, nameof(type));
foreach (var info in Schemas)
{
var o = info.GetDefaultValue(type);
if (o.HasValue)
{
return(o.Value);
}
}
if (type.IsEnum)
{
var mapValues = GetMapValues(type);
if (mapValues != null)
{
var fields =
from f in mapValues
where f.MapValues.Any(a => a.Value == null)
select f.OrigValue;
var value = fields.FirstOrDefault();
if (value != null)
{
SetDefaultValue(type, value);
return(value);
}
}
}
return(DefaultValue.GetValue(type, this));
}
public override Expression Reduce()
=> Constant(
_mappingSchema == null ?
DefaultValue.GetValue(Type) :
_mappingSchema.GetDefaultValue(Type),
Type);