/// <summary>
/// Evaluates the specified expression.
/// </summary>
/// <param name="expression">The expression to evaluate.</param>
/// <returns>Value of the expression.</returns>
public virtual QueryValue Visit(LinqDefaultIfEmptyExpression expression)
{
var source = this.EvaluateCollection(expression.Source);
if (source.Elements.Count == 0)
{
var elementType = source.Type.ElementType;
var queryClrType = elementType as IQueryClrType;
var queryScalarType = elementType as QueryScalarType;
QueryValue defaultValue;
if (expression.DefaultValue == null)
{
if (queryScalarType != null && queryClrType != null && typeof(ValueType).IsAssignableFrom(queryClrType.ClrType))
{
defaultValue = queryScalarType.CreateValue(Activator.CreateInstance(queryClrType.ClrType));
}
else
{
defaultValue = elementType.NullValue;
}
}
else
{
defaultValue = this.Evaluate(expression.DefaultValue);
}
return(source.Type.CreateCollectionWithValues(new QueryValue[] { defaultValue }));
}
return(source);
}
/// <summary>
/// Generates System.CodeDom.CodeExpression from the given expression.
/// </summary>
/// <param name="expression">Expression from which System.CodeDom.CodeExpression is generated.</param>
/// <returns>Generated System.CodeDom.CodeExpression.</returns>
public virtual CodeExpression Visit(LinqDefaultIfEmptyExpression expression)
{
CodeExpression source = this.GenerateCode(expression.Source);
if (expression.DefaultValue != null)
{
CodeExpression defaultValue = this.GenerateCode(expression.DefaultValue);
return(source.Call("DefaultIfEmpty", defaultValue));
}
else
{
return(source.Call("DefaultIfEmpty"));
}
}
/// <summary>
/// Resolves types for the specified expression.
/// </summary>
/// <param name="expression">The expression to resolve types for.</param>
/// <returns>Expression with resolved types.</returns>
public QueryExpression Visit(LinqDefaultIfEmptyExpression expression)
{
var source = this.ResolveTypes(expression.Source);
var sourceType = ValidateSourceIsACollection(source);
if (expression.DefaultValue != null)
{
var defaultValue = this.ResolveTypes(expression.DefaultValue);
return(new LinqDefaultIfEmptyExpression(source, sourceType, defaultValue));
}
else
{
return(new LinqDefaultIfEmptyExpression(source, sourceType));
}
}
/// <summary>
/// Replaces the given expression.
/// </summary>
/// <param name="expression">The root node of the expression tree being visited.</param>
/// <returns>Replaced expression.</returns>
public virtual QueryExpression Visit(LinqDefaultIfEmptyExpression expression)
{
QueryExpression source = this.ReplaceExpression(expression.Source);
if (expression.DefaultValue != null)
{
QueryExpression defaultValue = this.ReplaceExpression(expression.DefaultValue);
if (this.HasChanged(expression.Source, source) || this.HasChanged(expression.DefaultValue, defaultValue))
{
return(new LinqDefaultIfEmptyExpression(source, expression.ExpressionType, defaultValue));
}
}
if (this.HasChanged(expression.Source, source))
{
return(new LinqDefaultIfEmptyExpression(source, expression.ExpressionType));
}
return(expression);
}
/// <summary>
/// Visits a QueryExpression tree whose root node is the LinqDefaultIfEmptyExpression.
/// </summary>
/// <param name="expression">The root node of the expression tree being visited.</param>
/// <returns>Uri query string representing the expression.</returns>
public virtual string Visit(LinqDefaultIfEmptyExpression expression)
{
throw new TaupoNotSupportedException("Not supported");
}
