73 lines
2.5 KiB
C#
73 lines
2.5 KiB
C#
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using System.Linq.Expressions;
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namespace langguanApi.Extensions
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{
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/// <summary>
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/// linq extension
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/// </summary>
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public static class WhereIfExtension
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{
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public static IQueryable<T> WhereIf<T>(this IQueryable<T> source, bool condition, Expression<Func<T, bool>> predicate)
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{
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return condition ? source.Where(predicate) : source;
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}
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public static IQueryable<T> WhereIf<T>(this IQueryable<T> source, Expression<Func<T, int, bool>> predicate, bool condition)
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{
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return condition ? source.Where(predicate) : source;
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}
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public static IEnumerable<T> WhereIf<T>(this IEnumerable<T> source, bool condition, Func<T, bool> predicate)
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{
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return condition ? source.Where(predicate) : source;
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}
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public static Expression<Func<T, bool>> And<T>(
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this Expression<Func<T, bool>> first,
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Expression<Func<T, bool>> second)
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{
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return first.AndAlso<T>(second, Expression.AndAlso);
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}
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/// <summary>
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/// 合并表达式以及参数
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/// </summary>
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/// <typeparam name="T"></typeparam>
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/// <param name="expr1"></param>
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/// <param name="expr2"></param>
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/// <param name="func"></param>
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/// <returns></returns>
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private static Expression<Func<T, bool>> AndAlso<T>(
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this Expression<Func<T, bool>> expr1,
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Expression<Func<T, bool>> expr2,
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Func<Expression, Expression, BinaryExpression> func)
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{
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var parameter = Expression.Parameter(typeof(T));
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var leftVisitor = new ReplaceExpressionVisitor(expr1.Parameters[0], parameter);
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var left = leftVisitor.Visit(expr1.Body);
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var rightVisitor = new ReplaceExpressionVisitor(expr2.Parameters[0], parameter);
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var right = rightVisitor.Visit(expr2.Body);
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return Expression.Lambda<Func<T, bool>>(
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func(left, right), parameter);
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}
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private class ReplaceExpressionVisitor
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: ExpressionVisitor
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{
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private readonly Expression _oldValue;
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private readonly Expression _newValue;
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public ReplaceExpressionVisitor(Expression oldValue, Expression newValue)
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{
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_oldValue = oldValue;
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_newValue = newValue;
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}
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public override Expression Visit(Expression node)
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{
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if (node == _oldValue)
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return _newValue;
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return base.Visit(node);
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}
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}
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}
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}
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