![](/img/trans.png)
[英]How to write below mysql query using Entity Framework with Lambda expression?
[英]How can I optimise this lambda expression to query using entity framework for each row that contains a list of words?
我有一些意見,如: "Steve Brian McFistycuffs Johnson"
我想查看我的數據庫,並以任何順序返回包含這些單詞的所有記錄。
我做的是什么
var matches = myContext.MyTable.Where( c => c.Name.Contains("Steve") && c.Name.Contains("Brian") && c.Name.Contains("McFistycuffs") && c.Name.Conains("Johnson"));
但是我需要動態地執行此操作,並且單詞的數量可能會發生變化。
我還想確保無論我選擇什么,它都不會影響實體框架創建SQL語句,例如。 我想確保盡可能優化它。 這意味着在lambda中做某種foreach可能不會起作用,因為實體框架不能輕易地將它映射到SQL。
有什么建議么?
就像是:
static void Main()
{
string[] words = {"abc", "def"};
var filter = ContainsAllWords<Person>(x => x.Name, words);
// same as: x => x.Name.Contains("abc") && x.Name.Contains("def")
// then:
var rows = myContext.MyTable.Where(filter);
}
static Expression<Func<T,bool>> ContainsAllWords<T>(
Expression<Func<T, string>> selector, string[] words)
{
if (words == null || words.Length == 0) return x => true;
Expression body = Expression.Call(selector.Body, "Contains", null,
Expression.Constant(words[0], typeof(string)));
for (int i = 1; i < words.Length; i++)
{
body = Expression.AndAlso(body,
Expression.Call(selector.Body, "Contains", null,
Expression.Constant(words[i], typeof(string))));
}
return Expression.Lambda<Func<T, bool>>(body, selector.Parameters);
}
var list = new[] { "Brian", "Steve", "Johnson" };
var x = myContext.MyTable.Where(c => list.All(p => c.Name.Contains(p)))
str = "Steve Brian McFistycuffs Johnson"
string[] strParts = str.Split(' ');
myContext.MyTable.Where(c => strParts.All(part => c.Name.contains(part )))
var arr = new string[] {"Steve","Brian","McFistycuffs","Johnson"};
var matches = myContext.MyTable.Where(c =>arr.All(ar => ar==c.Name));
以下幾行可能是什么?
string inputFull = "Steve Brian McFistycuffs Johnson";
string[] stringSeparators = new string[] {" "};
var matches = myContext.MyTable;
foreach(string input in inputFull.Split(stringSeparators, StringSplitOptions.None))
{
matches = matches.Where(c => c.Name.Contains("input"))
}
編輯:使用上面的答案中的.All()會更好。
只是一個瘋狂的猜測..如何使用正則表達式?
(代碼尚未測試)
var input = "Steve Brian McFistycuffs Johnson";
var re = new Regex(input.Replace(" ","|"));
var matches = myContext.MyTable.Where( c => re.IsMatch(c.Name));
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.