/// <summary>
/// Rewrites a projection that produces a single member to a projection that produces a member of type ColumnSettings.
/// </summary>
/// <param name="expression">Projector.</param>
/// <returns>A modified expression if projection produces a single member; otherwise the same expression.</returns>
public override Expression Rewrite(Expression expression)
{
var lambda = (LambdaExpression)expression;
var compositeTypeVisitor = new CompositeTypeVisitor();
compositeTypeVisitor.Visit(lambda);
if (compositeTypeVisitor.IsProjectingACompositeType)
{
return(expression);
}
Expression projection = null;
_expressions = new List <Expression>();
try
{
Visit(lambda.Body);
if (_expressions.Count == 1)
{
MemberExpression memberExp = (MemberExpression)_expressions[0];
string propertyName = memberExp.Member.Name;
var columnSettings = ((ColumnSettings)typeof(ColumnSettings)
.GetMethod("Build")
.MakeGenericMethod(new Type[] { lambda.Body.Type })
.Invoke(null, new object[] { Expression.Lambda(lambda.Body) }))
.Name(propertyName);
projection = Expression.Constant(columnSettings, typeof(ColumnSettings));
}
else if (_expressions.Count > 1)
{
throw new InvalidProjectionException("There are multiple members across the projection. Ensure you project a single member, otherwise wrap it using a new operator.", lambda.Body);
}
}
finally
{
_expressions = null;
}
if (projection == null)
{
return(expression);
}
return(Expression.Lambda(projection, lambda.Parameters));
}
/// <summary>
/// Checks whether the projection is valid or not. A projection is valid if it's a flat projection and references at least one time the projector's parameter.
/// </summary>
/// <param name="expression">Projector.</param>
public void Validate(Expression expression)
{
// Checks if the lambda's expression parameter is referenced within the projection
var paramProjectionValidator = new ParameterReferencesValidator();
paramProjectionValidator.Validate(expression);
// Determines if the projection denotes a composite type or not
var compositeTypeVisitor = new CompositeTypeVisitor();
compositeTypeVisitor.Visit(expression);
if (!compositeTypeVisitor.IsProjectingACompositeType)
{
// It's a single member projection, so it checks if the ColumnSettings has a name set
var columnSettingsProjValidator = new ColumnSettingsNameValidator();
columnSettingsProjValidator.Validate(expression);
}
else
{
var flatProjectionValidator = new FlatProjectionValidator();
flatProjectionValidator.Validate(expression);
}
}
