/// <summary>
/// 转换 Lambda 表达式中的第一个参数为 <param name="targetElementType"/> 类型。
/// </summary>
/// <param name="lambda">需要转换的原始表达式树。</param>
/// <param name="targetElementType">需要转换的目标元素类型。</param>
/// <returns>转换完成的目标表达式树。</returns>
public static LambdaExpression ChangeParameter(this LambdaExpression lambda, Type targetElementType)
{
var originalParameter = lambda.Parameters[0];
var parameterExpr = Expression.Parameter(targetElementType, originalParameter.Name);
var builder = new ExpresionRewriteBuilder(originalParameter.Type, targetElementType);
var value = builder.Build(lambda.Body, expr =>
{
if (!(expr is ParameterExpression))
{
return(expr);
}
var pe = expr as ParameterExpression;
if (pe.Name == parameterExpr.Name && pe.Type == parameterExpr.Type)
{
return(parameterExpr);
}
else
{
return(expr);
}
});
var result = Expression.Lambda(value, parameterExpr);
return(result);
}
/// <summary>
/// 为数据源附加查询。
/// </summary>
/// <param name="originalElementType">附加查询的原始元素类型。</param>
/// <param name="targetExpr">附加查询表达式树。</param>
/// <returns>一个附加完成的查询分析器接口。</returns>
public IQueryableParser Attach(Type originalElementType, Expression targetExpr)
{
var builder = new ExpresionRewriteBuilder(originalElementType, DataSource.ElementType);
var parser = new QueryableParser {
DataSource = DataSource,
};
parser.Converter = p =>
{
if (p is UnaryExpression)
{
p = (p as UnaryExpression).Operand;
}
if (!(p is LambdaExpression))
{
throw new NotSupportedException();
}
var lambda = p as LambdaExpression;
var @parameters = lambda.Parameters.Where(r => r.Type == builder.SourceType).ToArray();
if ([email protected]())
{
return(p);
}
if (@parameters.Count() > 1)
{
throw new NotSupportedException();
}
var parameterExpr = Expression.Parameter(DataSource.ElementType, @parameters[0].Name);
var value = builder.Build(lambda.Body, expr =>
{
if (!(expr is ParameterExpression))
{
return(expr);
}
var pe = expr as ParameterExpression;
if (pe.Name == parameterExpr.Name && pe.Type == parameterExpr.Type)
{
return(parameterExpr);
}
else
{
return(expr);
}
});
var result = Expression.Lambda(value, parameterExpr);
return(result);
};
parser.Build(targetExpr as MethodCallExpression);
return(parser);
}
