Linq TO Entity Or Linq TO EF 中的where引數化查詢
阿新 • • 發佈:2018-12-20
注意:使用時注意修改名稱空間using System; using System.Linq.Expressions; namespace Utils { /// <summary> /// 統一ParameterExpression /// </summary> public class ParameterReplacer : ExpressionVisitor { public ParameterReplacer(ParameterExpression paramExpr) { this.ParameterExpression = paramExpr; } public ParameterExpression ParameterExpression { get; private set; } public Expression Replace(Expression expr) { return this.Visit(expr); } protected override Expression VisitParameter(ParameterExpression p) { return this.ParameterExpression; } } public static class PredicateExtensionses { public static Expression<Func<T, bool>> True<T>() { return f => true; } public static Expression<Func<T, bool>> False<T>() { return f => false; } public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right) { var candidateExpr = Expression.Parameter(typeof(T), "candidate"); var parameterReplacer = new ParameterReplacer(candidateExpr); var left = parameterReplacer.Replace(exp_left.Body); var right = parameterReplacer.Replace(exp_right.Body); var body = Expression.And(left, right); return Expression.Lambda<Func<T, bool>>(body, candidateExpr); } public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right) { var candidateExpr = Expression.Parameter(typeof(T), "candidate"); var parameterReplacer = new ParameterReplacer(candidateExpr); var left = parameterReplacer.Replace(exp_left.Body); var right = parameterReplacer.Replace(exp_right.Body); var body = Expression.Or(left, right); return Expression.Lambda<Func<T, bool>>(body, candidateExpr); } } }