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    <p>Well, you can use <code>Expression.AndAlso</code> / <code>OrElse</code> etc to combine logical expressions, but the problem is the parameters; are you working with the same <code>ParameterExpression</code> in expr1 and expr2? If so, it is easier:</p> <pre><code>var body = Expression.AndAlso(expr1.Body, expr2.Body); var lambda = Expression.Lambda&lt;Func&lt;T,bool&gt;&gt;(body, expr1.Parameters[0]); </code></pre> <p>This also works well to negate a single operation:</p> <pre><code>static Expression&lt;Func&lt;T, bool&gt;&gt; Not&lt;T&gt;( this Expression&lt;Func&lt;T, bool&gt;&gt; expr) { return Expression.Lambda&lt;Func&lt;T, bool&gt;&gt;( Expression.Not(expr.Body), expr.Parameters[0]); } </code></pre> <p>Otherwise, depending on the LINQ provider, you might be able to combine them with <code>Invoke</code>:</p> <pre><code>// OrElse is very similar... static Expression&lt;Func&lt;T, bool&gt;&gt; AndAlso&lt;T&gt;( this Expression&lt;Func&lt;T, bool&gt;&gt; left, Expression&lt;Func&lt;T, bool&gt;&gt; right) { var param = Expression.Parameter(typeof(T), "x"); var body = Expression.AndAlso( Expression.Invoke(left, param), Expression.Invoke(right, param) ); var lambda = Expression.Lambda&lt;Func&lt;T, bool&gt;&gt;(body, param); return lambda; } </code></pre> <p>Somewhere, I have got some code that re-writes an expression-tree replacing nodes to remove the need for <code>Invoke</code>, but it is quite lengthy (and I can't remember where I left it...)</p> <hr> <p>Generalized version that picks the simplest route:</p> <pre><code>static Expression&lt;Func&lt;T, bool&gt;&gt; AndAlso&lt;T&gt;( this Expression&lt;Func&lt;T, bool&gt;&gt; expr1, Expression&lt;Func&lt;T, bool&gt;&gt; expr2) { // need to detect whether they use the same // parameter instance; if not, they need fixing ParameterExpression param = expr1.Parameters[0]; if (ReferenceEquals(param, expr2.Parameters[0])) { // simple version return Expression.Lambda&lt;Func&lt;T, bool&gt;&gt;( Expression.AndAlso(expr1.Body, expr2.Body), param); } // otherwise, keep expr1 "as is" and invoke expr2 return Expression.Lambda&lt;Func&lt;T, bool&gt;&gt;( Expression.AndAlso( expr1.Body, Expression.Invoke(expr2, param)), param); } </code></pre> <p>Starting from .net 4.0. There is the ExpressionVistor class which allows you to build expressions that are EF safe.</p> <pre><code> public static Expression&lt;Func&lt;T, bool&gt;&gt; AndAlso&lt;T&gt;( this Expression&lt;Func&lt;T, bool&gt;&gt; expr1, Expression&lt;Func&lt;T, bool&gt;&gt; expr2) { var parameter = Expression.Parameter(typeof (T)); var leftVisitor = new ReplaceExpressionVisitor(expr1.Parameters[0], parameter); var left = leftVisitor.Visit(expr1.Body); var rightVisitor = new ReplaceExpressionVisitor(expr2.Parameters[0], parameter); var right = rightVisitor.Visit(expr2.Body); return Expression.Lambda&lt;Func&lt;T, bool&gt;&gt;( Expression.AndAlso(left, right), parameter); } private class ReplaceExpressionVisitor : ExpressionVisitor { private readonly Expression _oldValue; private readonly Expression _newValue; public ReplaceExpressionVisitor(Expression oldValue, Expression newValue) { _oldValue = oldValue; _newValue = newValue; } public override Expression Visit(Expression node) { if (node == _oldValue) return _newValue; return base.Visit(node); } } </code></pre>
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    1. POCombining two expressions (Expression<Func<T, bool>>)
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    1. USMarc Gravell
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    1. POCombining two expressions (Expression<Func<T, bool>>)
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    1. COHey Marc, I tried out your first suggestion, in the your first code block above, but when I pass in the "lambda" expression<func<T,bool>> result in a Where method, I get an error saying the parameter is out of scope? any idea? cheers
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    2. CO@Andy - yes (see the first sentence) - you will get this if you are using different parameter instances in the two versions... I'll update with another option (but which doesn't work for all providers; LINQ-to-Objects and LINQ-to-SQL will be fine, but EF won't be...)
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    3. COD'oh! I've already covered this in the second version... it can be simplified a little bit, though (will update)
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