如何將多個部分linq組合成一個查詢？

Question

運算符應為“AND”而不是“OR”。

我試圖重構以下代碼，我理解以下編寫linq查詢的方式可能不是正確的方法。 可以告訴我如何將以下內容組合成一個查詢。

  AllCompany.Where(itm => itm != null).Distinct().ToList(); if (AllCompany.Count > 0) { //COMPANY NAME if (isfldCompanyName) { AllCompany = AllCompany.Where(company => company["Company Name"].StartsWith(fldCompanyName)).ToList(); } //SECTOR if (isfldSector) { AllCompany = AllCompany.Where(company => fldSector.Intersect(company["Sectors"].Split('|')).Any()).ToList(); } //LOCATION if (isfldLocation) { AllCompany = AllCompany.Where(company => fldLocation.Intersect(company["Location"].Split('|')).Any()).ToList(); } //CREATED DATE if (isfldcreatedDate) { AllCompany = AllCompany.Where(company => company.Statistics.Created >= createdDate).ToList(); } //LAST UPDATED DATE if (isfldUpdatedDate) { AllCompany = AllCompany.Where(company => company.Statistics.Updated >= updatedDate).ToList(); } //Allow Placements if (isfldEmployerLevel) { fldEmployerLevel = (fldEmployerLevel == "Yes") ? "1" : ""; AllCompany = AllCompany.Where(company => company["Allow Placements"].ToString() == fldEmployerLevel).ToList(); } 

Answer 1

首先，除非AllCompany屬於某種神奇的自定義類型，否則第一行不會給你任何東西。 另外，我懷疑Distinct運作方式與你想要的一樣。 我不知道AllCompany的類型，但我猜它只給你參考區別。

無論哪種方式，我想你想要的：

fldEmployerLevel = (fldEmployerLevel == "Yes") ? "1" : "";

var result = AllCompany.Where(itm => itm != null)
    .Where(company => !isfldCompanyName || company["Company Name"].StartsWith(fldCompanyName))
    .Where(company => !isfldSector|| fldSector.Intersect(company["Sectors"].Split('|')).Any())
    .Where(company => !isfldLocation|| fldLocation.Intersect(company["Location"].Split('|')).Any())
    .Where(company => !isfldcreatedDate|| company.Statistics.Created >= createdDate)
    .Where(company => !isfldUpdatedDate|| company.Statistics.Updated >= updatedDate)
    .Where(company => !isfldEmployerLevel|| company["Allow Placements"].ToString() == fldEmployerLevel)
    .Distinct()
    .ToList();

編輯：

我將Distinct移到查詢的末尾以優化處理。

Answer 2

怎么樣這樣做;

AllCompany = AllCompany .Where(company => (company => company.Statistics.Created >= createdDate)) && (company.Statistics.Updated >= updatedDate));

如果查詢的每個部分都是可選的（如創建日期，最后更新日期..），那么您可以構建linq查詢字符串。

Answer 3

這是一個偷偷摸摸的伎倆。 如果在其自己的靜態類中定義以下擴展方法：

public virtual IEnumerable<T> WhereAll(params Expression<Predicate<T> filters)
{
    return filters.Aggregate(dbSet, (acc, element) => acc.Where(element));
}

然后你可以寫

var result = AllCompany.WhereAll(itm => itm != null,
    company => !isfldCompanyName || company["Company Name"].StartsWith(fldCompanyName),
    company => !isfldSectorn || fldSector.Intersect(company["Sectors"].Split('|')).Any(),
    company => !isfldLocation || fldLocation.Intersect(company["Location"].Split('|')).Any(),
    company => !isfldcreatedDate || company.Statistics.Created >= createdDate,
    company => !isfldUpdatedDate || company.Statistics.Updated >= updatedDate,
    company => !isfldEmployerLevel || company["Allow Placements"].ToString() == fldEmployerLevel)
    .Distinct()
    .ToList();