Question

我想要从中返回查询 WANOM_DETAILS & STRDT tables where PIPELINE = 'F' AND HISTORICAL_FLAG <> 'T' AND INSTALLATION = 'EA' AND ANOMALY_CLASS = 'Critical'。

if语句正常工作，但目前只返回查询 WANOM_DETAILS & STRDT tables where ANOMALY_CLASS = 'Critical'因为这是model.ToList();

之前的最后一行

非常感谢任何帮助。这是代码;

        strdt = "EA";
        anom_class = "Critical";

        var models = db.WANOM_DETAILS;

        var model = models.Where(wanom_details => wanom_details.STRDT.PIPELINE == "F");
        model = models.Where(wanom_details => wanom_details.STRDT.HISTORICAL_FLAG != "T");
        if (strdt != "")
        {
            model = models.Where(wanom_details => wanom_details.INSTALLATION == strdt);
        }
        if (anom_class != "")
        {
            model = models.Where(wanom_details => wanom_details.ANOMALY_CLASS == anom_class);
        }
        if (subdt != "")
        {
            model = models.Where(wanom_details => wanom_details.WANOM.SUBSTRUCTURE == subdt);
        }
        if (comp != "")
        {
            model = models.Where(wanom_details => wanom_details.WANOM.TYPE + "-" + wanom_details.WANOM.IDENT == comp);
        }

        return PartialView("_SiteAnomalyGridViewPartial", model.ToList());

Answer 1

你可以将Where的结果链接起来，所以：

X.Where(x => x.Prop > 1 && x.Prop2 == "1")

你可以实现两个Where的相同结果连接：

X.Where(x => x.Prop > 1).Where(x.Prop2 == "1").

所以在你的情况下你可以这样做：

strdt = "EA";
anom_class = "Critical";

var models = db.WANOM_DETAILS;

models = models.Where(wanom_details => wanom_details.STRDT.PIPELINE == "F");
models = models.Where(wanom_details => wanom_details.STRDT.HISTORICAL_FLAG != "T");
if (strdt != "")
{
    models = models.Where(wanom_details => wanom_details.INSTALLATION == strdt);
}
if (anom_class != "")
{
    models = models.Where(wanom_details => wanom_details.ANOMALY_CLASS == anom_class);
}
if (subdt != "")
{
    models = models.Where(wanom_details => wanom_details.WANOM.SUBSTRUCTURE == subdt);
}
if (comp != "")
{
    models = models.Where(wanom_details => wanom_details.WANOM.TYPE + "-" + wanom_details.WANOM.IDENT == comp);
}

return PartialView("_SiteAnomalyGridViewPartial", models.ToList());

编辑：

当你使用一个长Where表达式链接条件与&&运算符时，sql generetd根据条件And生成。但是，当您使用IQueryable表达式链接Where时，linq-to-sql genereate会为每个表达式选择where-where，并将所有内容包装在Union查询中。 db-server可能会优化，但对我来说这感觉很尴尬。要获得第一个结果，您可以使用greate predicatebuilder扩展方法：

strdt = "EA";
anom_class = "Critical";

var predicate = PredicateBuilder.False<ClassOfWANOM_DETAILS>();

predicate.And(wanom_details => wanom_details.STRDT.PIPELINE == "F");
predicate.And(wanom_details => wanom_details.STRDT.HISTORICAL_FLAG != "T");
if (strdt != "")
    predicate.And(wanom_details => wanom_details.INSTALLATION == strdt);
if (anom_class != "")
    predicate.And(wanom_details => wanom_details.ANOMALY_CLASS == anom_class);
if (subdt != "")
    predicate.And(wanom_details => wanom_details.WANOM.SUBSTRUCTURE == subdt);
if (comp != "")
    predicate.And(wanom_details => wanom_details.WANOM.TYPE + "-" + wanom_details.WANOM.IDENT == comp);

return PartialView("_SiteAnomalyGridViewPartial", db.WANOM_DETAILS.Where(predicate).ToList());

linq - multiple where语句，如果变量不为null

1 个答案:

编辑：