protected override Expression VisitLike(QueryTranslatorContext context, LikeExpression expression)
{
// Is the left side a collection?
if (expression.Left is CollectionExpression collection)
{
// Build the collection accessor parameter.
var parameter = collection.Accept(this, context);
// Build the predicate expression.
context.PushParameter(collection.ItemType);
var predicate = Expression.Lambda(
new LikeExpression(
collection.ItemAccessor,
expression.Right).Accept(this, context),
context.Parameter);
context.PopParameter();
// We need to use an Enumerable.Any together with the LIKE predicate.
return(Expression.Call(typeof(Enumerable), "Any", new Type[] { collection.ItemType }, parameter, predicate));
}
var left = expression.Left.Accept(this, context);
var right = expression.Right.Accept(this, context);
return(Expression.Call(
null, typeof(DbFunctionsExtensions).GetMethod("Like", new[] { typeof(DbFunctions), typeof(string), typeof(string) }),
Expression.Constant(EF.Functions), left, right));
}
protected override Expression VisitRelational(QueryTranslatorContext context, RelationalExpression expression)
{
var left = expression.Left.Accept(this, context);
var right = expression.Right.Accept(this, context);
switch (expression.Operator)
{
case RelationalOperator.EqualTo:
return(Expression.Equal(left, right));
case RelationalOperator.NotEqualTo:
return(Expression.NotEqual(left, right));
case RelationalOperator.GreaterThan:
return(Expression.GreaterThan(left, right));
case RelationalOperator.GreaterThanOrEqualTo:
return(Expression.GreaterThanOrEqual(left, right));
case RelationalOperator.LessThan:
return(Expression.LessThan(left, right));
case RelationalOperator.LessThanOrEqualTo:
return(Expression.LessThanOrEqual(left, right));
}
throw new InvalidOperationException($"Unknown operator '{expression.Operator}'.");
}
protected override Expression VisitCollection(QueryTranslatorContext context, CollectionExpression expression)
{
var properties = new Queue <PropertyInfo>(expression.Properties);
var accessor = Expression.MakeMemberAccess(context.Parameter, properties.Dequeue());
while (properties.Count > 0)
{
accessor = Expression.MakeMemberAccess(accessor, properties.Dequeue());
}
return(accessor);
}
protected override Expression VisitRelation(QueryTranslatorContext context, RelationalExpression expression)
{
// Is the left side a collection?
if (expression.Left is CollectionExpression collection)
{
// Build the collection accessor parameter.
var parameter = collection.Accept(this, context);
// Build the predicate expression.
context.PushParameter(collection.ItemType);
var predicate = Expression.Lambda(
new RelationalExpression(
collection.ItemAccessor,
expression.Right,
expression.Operator).Accept(this, context),
context.Parameter);
context.PopParameter();
// Combine them into an Enumerable.Any or Enumerable.All call.
var method = expression.Operator == RelationalOperator.NotEqualTo ? "All" : "Any";
return(Expression.Call(typeof(Enumerable), method, new Type[] { collection.ItemType }, parameter, predicate));
}
var left = expression.Left.Accept(this, context);
var right = expression.Right.Accept(this, context);
switch (expression.Operator)
{
case RelationalOperator.EqualTo:
return(Expression.Equal(left, right));
case RelationalOperator.NotEqualTo:
return(Expression.NotEqual(left, right));
case RelationalOperator.GreaterThan:
return(Expression.GreaterThan(left, right));
case RelationalOperator.GreaterThanOrEqualTo:
return(Expression.GreaterThanOrEqual(left, right));
case RelationalOperator.LessThan:
return(Expression.LessThan(left, right));
case RelationalOperator.LessThanOrEqualTo:
return(Expression.LessThanOrEqual(left, right));
}
throw new InvalidOperationException($"Unknown operator '{expression.Operator}'.");
}
public static Expression <Func <TEntity, bool> > Translate(QueryExpression query)
{
if (query == null)
{
return(_ => true);
}
// Translate the query expression to a LINQ expression.
var visitor = new QueryTranslator <TContext, TEntity>();
var context = new QueryTranslatorContext(typeof(TEntity));
var expression = query.Accept(visitor, context);
// Parse the expression and rewrite it.
return(Expression.Lambda <Func <TEntity, bool> >(expression, context.Parameter));
}
protected override Expression VisitProperty(QueryTranslatorContext context, PropertyExpression expression)
{
var parameter = expression.EntityType != context.Type
? (Expression)Expression.Convert(context.Parameter, expression.EntityType)
: context.Parameter;
var properties = new Queue <PropertyInfo>(expression.Properties);
var current = Expression.MakeMemberAccess(parameter, properties.Dequeue());
while (properties.Count > 0)
{
current = Expression.MakeMemberAccess(current, properties.Dequeue());
}
return(current);
}
public static Expression <Func <TEntity, bool> > Translate(QueryExpression query)
{
if (query == null)
{
var result = Expression.Constant(true);
return(_ => true);
}
// Define the parameter that will be used with out lambda expression.
var parameter = Expression.Parameter(typeof(TEntity), "entity");
// Translate the query expression to a LINQ expression.
var visitor = new QueryTranslator <TContext, TEntity>();
var context = new QueryTranslatorContext(parameter);
var expression = query.Accept(visitor, context);
// Parse the expression and rewrite it.
return(Expression.Lambda <Func <TEntity, bool> >(expression, parameter));
}
protected override Expression VisitScope(QueryTranslatorContext context, ScopeExpression expression)
{
return(expression.Expression.Accept(this, context));
}
protected override Expression VisitProperty(QueryTranslatorContext context, PropertyExpression expression)
{
return(Expression.Property(context.Parameter, expression.Name));
}
protected override Expression VisitOr(QueryTranslatorContext context, OrExpression expression)
{
return(Expression.OrElse(
expression.Left.Accept(this, context),
expression.Right.Accept(this, context)));
}
protected override Expression VisitNot(QueryTranslatorContext context, NotExpression expression)
{
return(Expression.Not(expression.Expression.Accept(this, context)));
}
protected override Expression VisitConversion(QueryTranslatorContext context, ConvertExpression expression)
{
return(Expression.Convert(expression.Expression.Accept(this, context), expression.Type));
}
protected override Expression VisitConstant(QueryTranslatorContext context, Expressions.Ast.ConstantExpression expression)
{
return(Expression.Constant(expression.Value));
}
protected override Expression VisitAnd(QueryTranslatorContext context, AndExpression expression)
{
return(Expression.AndAlso(
expression.Left.Accept(this, context),
expression.Right.Accept(this, context)));
}
