--- title: Handling Relationships in Dapper | daily.dev description: Covers how to map one-to-one, one-to-many, and many-to-many relationships in Dapper using QueryAsync with multiple type parameters and the splitOn parameter.... canonical: https://daily.dev/posts/handling-relationships-in-dapper-2pgxzo4h0 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Handling Relationships in Dapper | daily.dev og:description: Covers how to map one-to-one, one-to-many, and many-to-many relationships in Dapper using QueryAsync with multiple type parameters and the splitOn parameter.... og:url: https://daily.dev/posts/handling-relationships-in-dapper-2pgxzo4h0 og:image: https://api.daily.dev/og/posts/2pgXZo4h0.png og:image:alt: Handling Relationships in Dapper og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Handling Relationships in Dapper **[NikolaTech](https://daily.dev/sources/nikolatech)** · 6 min read · 0 upvotes · 0 comments ## Summary Covers how to map one-to-one, one-to-many, and many-to-many relationships in Dapper using QueryAsync with multiple type parameters and the splitOn parameter. Shows SQL joins paired with C# code, and explains the dictionary pattern needed to avoid duplicate parent objects when joining one-to-many or many-to-many data. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### How do I map a one-to-many relationship with Dapper without getting duplicate parent objects? Use a dictionary keyed by the parent entity's id when calling QueryAsync with a LEFT JOIN. For each row, check if the parent already exists in the dictionary; if not, add it and initialize its child list, then append the related child record to that existing instance's list, repeating for every row in the result set. _Developers wiring up Dapper joins can save this pattern for the next one-to-many mapping headache on daily.dev._ ### What does the splitOn parameter do in Dapper's QueryAsync method? It tells Dapper where a new object begins in a joined query result. Dapper reads columns left to right filling the first object's properties, and when it hits a column matching the splitOn name (commonly 'Id'), it starts mapping subsequent columns to the next object type specified in the QueryAsync generic parameters. _Anyone debugging multi-table Dapper queries can keep mapping tricks like this handy via daily.dev._ ## Similar posts on daily.dev - [Dapper in Depth with ASP.NET Core 10](https://daily.dev/posts/dapper-in-depth-with-asp-net-core-10-oad4bk2bw) · C\# Corner · 1 upvotes · 0 comments - [How to Work With Dapper in .Net](https://daily.dev/posts/how-to-work-with-dapper-in-net-yzgrlyllb) · freeCodeCamp · 17 upvotes · 0 comments - [One-to-Many Relationships](https://daily.dev/posts/one-to-many-relationships-swnrc9u0p) · Larablog · 1 upvotes · 0 comments --- Tags: [#.net](https://daily.dev/tags/.net), [#sql](https://daily.dev/tags/sql), [#c#](https://daily.dev/tags/c#) [View this post on daily.dev](https://daily.dev/posts/handling-relationships-in-dapper-2pgxzo4h0) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Handling Relationships in Dapper","url":"https://daily.dev/posts/handling-relationships-in-dapper-2pgxzo4h0","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/handling-relationships-in-dapper-2pgxzo4h0"},"datePublished":"2026-10-04T13:06:58.274Z","dateModified":"2026-10-04T13:11:54.174Z","description":"Covers how to map one-to-one, one-to-many, and many-to-many relationships in Dapper using QueryAsync with multiple type parameters and the splitOn parameter....","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/5c48342e136c74d6c43fc658f12efd45?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/5c48342e136c74d6c43fc658f12efd45?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"NikolaTech","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"NikolaTech","logo":"https://media.daily.dev/image/upload/s--1h2fO6FL--/f_auto,q_auto/v1791119050/logos/nikolatech?_a=BAMAMicg0","url":"https://daily.dev/sources/nikolatech"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/handling-relationships-in-dapper-2pgxzo4h0","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":".net,sql,c#","timeRequired":"PT6M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"NikolaTech","item":"https://daily.dev/sources/nikolatech"},{"@type":"ListItem","position":3,"name":"Handling Relationships in Dapper"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/handling-relationships-in-dapper-2pgxzo4h0#faq","mainEntity":[{"@type":"Question","name":"How do I map a one-to-many relationship with Dapper without getting duplicate parent objects?","acceptedAnswer":{"@type":"Answer","text":"Use a dictionary keyed by the parent entity's id when calling QueryAsync with a LEFT JOIN. 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