private static Expression <T> Compose <T>(this Expression <T> first, Expression <T> second, Func <Expression, Expression, Expression> merge)
{
// build parameter map (from parameters of second to parameters of first)
var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
// replace parameters in the second lambda expression with parameters from the first
var secondBody = RebindParameterVisitor.ReplaceParameters(map, second.Body);
// apply composition of lambda expression bodies to parameters from the first expression
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
public static Expression <T> Compose <T>(
this Expression <T> first,
Expression <T> second,
Func <Expression, Expression, Expression> merge)
{
var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] })
.ToDictionary(p => p.s, p => p.f);
var secondBody = RebindParameterVisitor.ReplaceParameters(map, second.Body);
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
/// <summary>
/// Joins two binary lambda expressions using the 'Or' conditional operator.
/// </summary>
/// <typeparam name="T">
/// The type of the predicate.
/// </typeparam>
/// <param name="left">
/// The first <see cref="Expression{TDelegate}" />.
/// </param>
/// <param name="right">
/// The second <see cref="Expression{TDelegate}" />.
/// </param>
/// <returns>
/// The resulting <see cref="Expression{TDelegate}" /> object that contains the joined
/// <see cref="Expression{TDelegate}" /> objects.
/// </returns>
public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > left, Expression <Func <T, bool> > right)
{
Expression <Func <T, bool> > all = t => true;
if (left == all || right == all)
{
return(all);
}
var rightExprBody = new RebindParameterVisitor(right.Parameters[0], left.Parameters[0]).Visit(right.Body);
return(Expression.Lambda <Func <T, bool> >(Expression.OrElse(left.Body, rightExprBody ?? throw new InvalidOperationException()), left.Parameters));
}
/// <summary>
/// Joins two binary lambda expressions using the 'And' conditional operator.
/// </summary>
/// <typeparam name="T">
/// The type of the predicate.
/// </typeparam>
/// <param name="left">
/// The left <see cref="Expression{TDelegate}" />.
/// </param>
/// <param name="right">
/// The right <see cref="Expression{TDelegate}" />.
/// </param>
/// <returns>
/// The resulting <see cref="Expression{TDelegate}" /> object that contains the joined
/// <see cref="Expression{TDelegate}" /> objects.
/// </returns>
public static Expression <Func <T, bool> > And <T>(this Expression <Func <T, bool> > left, Expression <Func <T, bool> > right)
{
Expression <Func <T, bool> > all = t => true;
if (Lambda.ExpressionsEqual(left, all))
{
return(right);
}
if (Lambda.ExpressionsEqual(right, all))
{
return(left);
}
var rightExprBody = new RebindParameterVisitor(right.Parameters[0], left.Parameters[0]).Visit(right.Body);
return(Expression.Lambda <Func <T, bool> >(Expression.AndAlso(left.Body, rightExprBody ?? throw new InvalidOperationException()), left.Parameters));
}
/// <summary> OR </summary>
public static Expression <Func <T, bool> > Or <T>(
this Expression <Func <T, bool> > expr1,
Expression <Func <T, bool> > expr2)
{
if (expr1 is null)
{
throw new ArgumentNullException(nameof(expr1));
}
if (expr2 is null)
{
throw new ArgumentNullException(nameof(expr2));
}
var expr2Body = new RebindParameterVisitor(expr2.Parameters[0], expr1.Parameters[0])
.Visit(expr2.Body);
return(Expression.Lambda <Func <T, bool> >(
Expression.OrElse(expr1.Body, expr2Body), expr1.Parameters));
}
/// <summary> AND </summary>
public static Expression <Func <T, bool> > And <T>([NotNull] this Expression <Func <T, bool> > expr1, [NotNull] Expression <Func <T, bool> > expr2)
{
var expr2Body = new RebindParameterVisitor(expr2.Parameters[0], expr1.Parameters[0]).Visit(expr2.Body);
return(Expression.Lambda <Func <T, bool> >(Expression.AndAlso(expr1.Body, expr2Body), expr1.Parameters));
}
public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > expr1, Expression <Func <T, bool> > expr2)
{
var expr2Body = new RebindParameterVisitor(expr2.Parameters[0], expr1.Parameters[0]).Visit(expr2.Body);
return(Expression.Lambda <Func <T, bool> >(Expression.OrElse(expr1.Body, expr2Body), expr1.Parameters));
}
/// <summary>
/// 建立And查询条件
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="leftExpression">左表达式</param>
/// <param name="rightExpression">右表达式</param>
/// <returns>组合后的表达式</returns>
public static Expression <Func <T, bool> > And <T>([NotNull] this Expression <Func <T, bool> > leftExpression, [NotNull] Expression <Func <T, bool> > rightExpression)
{
var expr2Body = new RebindParameterVisitor(rightExpression.Parameters[0], leftExpression.Parameters[0]).Visit(rightExpression.Body);
return(Expression.Lambda <Func <T, bool> >(Expression.AndAlso(leftExpression.Body, expr2Body), leftExpression.Parameters));
}
/// <summary>
/// Joins two binary lambda expressions using the 'Or' conditional operator.
/// </summary>
/// <typeparam name="T">
/// The type of the predicate.
/// </typeparam>
/// <param name="left">
/// The first <see cref="Expression{TDelegate}" />.
/// </param>
/// <param name="right">
/// The second <see cref="Expression{TDelegate}" />.
/// </param>
/// <returns>
/// The resulting <see cref="Expression{TDelegate}" /> object that contains the joined
/// <see cref="Expression{TDelegate}" /> objects.
/// </returns>
public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > left, Expression <Func <T, bool> > right)
{
var leftExprBody = new RebindParameterVisitor(right.Parameters[0], left.Parameters[0]).Visit(right.Body);
return(Expression.Lambda <Func <T, bool> >(Expression.OrElse(left.Body, leftExprBody ?? throw new InvalidOperationException()), left.Parameters));
}